json_view: from_json() of the macros reads views directly

get<T>() and get_to() of a view call T's from_json() with the view itself
when that from_json() accepts views but not an unrelated probe type, and
fall back to materialize() otherwise. The from_json() functions of the
NLOHMANN_DEFINE_TYPE_*, NLOHMANN_DEFINE_DERIVED_TYPE_* and
NLOHMANN_JSON_SERIALIZE_ENUM(_STRICT) macros accept basic_json values and
views; a derived type whose base reads only json reads the base part
through materialize(). The library's own from_json() overloads are not
called with views: from_json() of a view (and of the probe) only looks up
functions by ADL.

New public trait nlohmann::is_json_view<T>, and the member type
basic_json_type of basic_json_view. With duplicate keys, the members of
such a T are those the view's lookups find (the first ones).

bench_decode.cpp measures decoding into structs (4-6x faster than
materialize().get<T>() on twitter, citm_catalog, and synthetic records).

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

.github/workflows/check_amalgamation.yml

@@ -163,9 +163,9 @@ jobs:
           python3 $GENERATOR --list-tags
           TAG_COUNT=$(python3 $GENERATOR --list-tags | wc -l)
 
-          python3 $GENERATOR --abi-tags diag,_dp,_vns --abi-tags _diag --output $RUNNER_TEMP/abi_tags.natvis
+          python3 $GENERATOR --abi-tags diag,_dp,_ns --abi-tags _diag --output $RUNNER_TEMP/abi_tags.natvis
-          grep -q '<!-- Namespace nlohmann::json_abi_diag_dp_vns -->' $RUNNER_TEMP/abi_tags.natvis
+          grep -q '<!-- Namespace nlohmann::json_abi_diag_dp_ns -->' $RUNNER_TEMP/abi_tags.natvis
-          grep -q '<!-- Namespace nlohmann::json_abi_diag_dp_vns_v[0-9_]* -->' $RUNNER_TEMP/abi_tags.natvis
+          grep -q '<!-- Namespace nlohmann::json_abi_diag_dp_ns_v[0-9_]* -->' $RUNNER_TEMP/abi_tags.natvis
           test $(grep -c '<!-- Namespace ' $RUNNER_TEMP/abi_tags.natvis) -eq $(( $(grep -c '<!-- Namespace ' nlohmann_json.natvis) + 2 ))
 
           python3 $GENERATOR --all --output $RUNNER_TEMP/all.natvis

FILES.md

@@ -309,7 +309,7 @@ The "Check amalgamation" workflow fails if the file is out of date.
 
 The file covers the namespace variants with up to two ABI tags. A Natvis file for other configurations can be
 generated with the `--abi-tags` or `--all` options, for example
-`make natvis NATVIS_ARGS="--abi-tags _diag,_dp,_vns --output my_nlohmann_json.natvis"`; see
+`make natvis NATVIS_ARGS="--abi-tags _diag,_dp,_ns --output my_nlohmann_json.natvis"`; see
 [`tools/generate_natvis`](tools/generate_natvis/README.md). With MSVC, CMake adds the file to the `nlohmann_json`
 target and installs it.
 

Makefile

@@ -120,7 +120,7 @@ $(AMALGAMATED_VIEW_FILE): $(SRCS)
 	tools/amalgamate/amalgamate.py -c tools/amalgamate/config_json_view.json -s . --verbose=yes
 
 NATVIS_VENV=tools/generate_natvis/venv
-# extra options for generate_natvis.py, e.g. NATVIS_ARGS="--abi-tags _diag,_dp,_vns --output my.natvis"
+# extra options for generate_natvis.py, e.g. NATVIS_ARGS="--abi-tags _diag,_dp,_ns --output my.natvis"
 NATVIS_ARGS=
 
 # regenerate nlohmann_json.natvis from the ABI tags and version in include/nlohmann/detail/abi_macros.hpp

docs/mkdocs/docs/api/basic_json_document/load.md

@@ -55,10 +55,7 @@ validate with overload 2 first, if the original vector must survive a failed loa
 
 ## Exceptions
 
-On a big-endian target, throws [`type_error.320`](../../home/exceptions.md#jsonexceptiontype_error320) -- the same
+Throws [`parse_error.116`](../../home/exceptions.md#jsonexceptionparse_error116) if `image` is not one
-exception [`save()`](save.md#exceptions) throws there, since the image format is little-endian only.
-
-Otherwise throws [`parse_error.116`](../../home/exceptions.md#jsonexceptionparse_error116) if `image` is not one
 `save()` could have written, or fails the requested `check`:
 
 | message               | when                                                                                                |
@@ -95,6 +92,9 @@ are checked once, however many nodes refer to it.
 
 ## Notes
 
+**Little-endian targets only.** On a big-endian target, `load()` does not exist, just like
+[`save()`](save.md#notes): the image format is little-endian, so a call fails to compile.
+
 ### `image_check` { #image_check }
 
 ```cpp

docs/mkdocs/docs/api/basic_json_document/save.md

@@ -31,9 +31,6 @@ Throws [`type_error.320`](../../home/exceptions.md#jsonexceptiontype_error320) i
 [discarded](is_discarded.md) -- a default-constructed document, or one a failed [`parse()`](parse.md)/
 [`read()`](read.md) with `allow_exceptions == false` left discarded.
 
-On a big-endian target, throws `type_error.320` with a different message instead: the image format is little-endian
-only (see [Notes](#notes)).
-
 Throws [`out_of_range.416`](../../home/exceptions.md#jsonexceptionout_of_range416) if the node count, the text, or
 the decoded strings of the image would individually reach 4 GiB -- the same 32-bit offsets
 [`parse()`](parse.md#exceptions) and, for edits, [`set`](set.md)/[`push_back`](push_back.md) are already limited to.
@@ -44,9 +41,6 @@ the decoded strings of the image would individually reach 4 GiB -- the same 32-b
     [json.exception.type_error.320] cannot save a discarded json_document
     ```
     ```
-    [json.exception.type_error.320] json_document images need a little-endian target
-    ```
-    ```
     [json.exception.out_of_range.416] images of 4 GiB or more are not supported by json_document
     ```
 
@@ -70,9 +64,9 @@ else -- see [`load`'s Exceptions](load.md#exceptions).
     the *same* build on the *same* (little-endian) machine -- not as a long-term storage format. Keep the original
     JSON text if you need to read a saved document back with a future library version.
 
-**Little-endian only.** The image is written as raw little-endian bytes, with no byte-swapping. `save()` (and
+**Little-endian targets only.** The image is written as raw little-endian bytes, with no byte-swapping. On a
-[`load`](load.md)) throw `type_error.320` on a big-endian target rather than silently produce bytes a big-endian
+big-endian target, `save()` and [`load`](load.md) do not exist: a call fails to compile rather than produce bytes a
-reader could not interpret correctly.
+big-endian reader could not interpret correctly.
 
 ## Examples
 

docs/mkdocs/docs/api/basic_json_view/get.md

@@ -27,8 +27,25 @@ For the types below, the conversion works directly on the flat index -- no `Basi
   [`materialize()`](materialize.md)) does; `#!cpp std::map<std::string, basic_json_view>` keeps views of the members
   instead of values
 
-Every other `T` -- `#!cpp std::list`, `#!cpp std::pair`, `#!cpp std::array`, enumerations, user types with a
+A default-constructible `T` whose `from_json()` accepts views reads the view directly as well, member by member, without
-`from_json()`, ... -- is converted by `#!cpp materialize().get<T>()`: the subtree is built into a real `BasicJsonType`
+building a `BasicJsonType` value. This covers the types of the
+[`NLOHMANN_DEFINE_TYPE_*`](../macros/nlohmann_define_type_intrusive.md) and
+[`NLOHMANN_DEFINE_DERIVED_TYPE_*`](../macros/nlohmann_define_derived_type.md) macros and the enumerations of
+[`NLOHMANN_JSON_SERIALIZE_ENUM`](../macros/nlohmann_json_serialize_enum.md), and any `from_json()` constrained to
+accept views, e.g. with [`is_json_view`](../is_json_view.md). A `from_json()` that also accepts types that are no JSON
+values at all, such as the unconstrained `#!cpp template<typename BasicJsonType> void from_json(const BasicJsonType&,
+T&)` of [arbitrary type conversions](../../features/arbitrary_types.md), is not called with a view: it may use
+`BasicJsonType` functions a view does not have. See [json_view](../../features/json_view.md).
+
+!!! warning "Duplicate keys"
+
+    Such a `from_json()` looks members up in the view, where a repeated key finds the **first** member, while
+    `#!cpp materialize().get<T>()` sees the **last** one, as [`BasicJsonType::parse()`](../basic_json/parse.md)
+    keeps it: for `#!cpp {"x":1,"x":2}`, `#!cpp get<point>()` reads `#!cpp x == 1`. See
+    [Duplicate keys](../../features/json_view.md#duplicate-keys).
+
+Every other `T` -- `#!cpp std::list`, `#!cpp std::pair`, `#!cpp std::array`, user types whose `from_json()` is
+written for `BasicJsonType` only, ... -- is converted by `#!cpp materialize().get<T>()`: the subtree is built into a real `BasicJsonType`
 value first (as [`BasicJsonType::parse()`](../basic_json/parse.md) would), and converted from there exactly as
 [`BasicJsonType::get<T>()`](../basic_json/get.md) would convert it.
 
@@ -55,10 +72,13 @@ Strong guarantee: there are no changes to the view or the document it refers to.
   an element to `U` throws.
 - For `#!cpp std::map`/`#!cpp std::unordered_map`: throws `type_error.302` if the value is not an object; otherwise,
   whatever converting a member to the mapped type throws.
+- For a `T` whose `from_json()` reads the view: whatever that `from_json()` throws; for the macros, the same
+  exceptions with the same messages as [`BasicJsonType::get<T>()`](../basic_json/get.md) of the same value.
 - For every other `T`: whatever [`materialize().get<T>()`](../basic_json/get.md) throws -- typically `type_error.302`,
   or whatever a user-provided `from_json()` throws.
 
-None of the exceptions thrown directly by this function (the first three bullets above) carry a
+None of the exceptions thrown directly by this function or by a `from_json()` that reads the view (the first four
+bullets above) carry a
 [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) path: the view has no `BasicJsonType` value to point at. An
 exception thrown while converting through `materialize()` (the last bullet) is different: it is thrown by a real
 `BasicJsonType` value, so it **does** carry a `JSON_DIAGNOSTICS` path if `BasicJsonType` was built with it enabled.
@@ -76,6 +96,8 @@ document.
 - `#!cpp std::map`/`#!cpp std::unordered_map`: linear in the number of members for walking them, plus the container's
   own insertion cost per member (logarithmic for `#!cpp std::map`, amortized constant for `#!cpp
   std::unordered_map`), times the complexity of converting one member to the mapped type.
+- a `T` whose `from_json()` reads the view: the cost of that `from_json()`; for the macros, linear in the number of
+  members times the cost of a lookup, plus the cost of converting the members.
 - every other `T`: the cost of [`materialize()`](materialize.md) and of destroying the `BasicJsonType` value
   afterwards, plus that of [`BasicJsonType::get<T>()`](../basic_json/get.md).
 

docs/mkdocs/docs/api/basic_json_view/get_to.md

@@ -5,12 +5,14 @@ template<typename T>
 T& get_to(T& v) const;
 ```
 
-Converts the value to `T` and stores it in `v`, in one of two ways:
+Converts the value to `T` and stores it in `v`, in one of three ways:
 
 - For the types that [`get<T>()`](get.md) converts directly -- arithmetic types, `#!cpp bool`,
   `#!cpp std::nullptr_t`, [`string_view_t`](index.md#member-types), `#!cpp std::basic_string`, `BasicJsonType`,
   `basic_json_view`, `#!cpp std::vector`, and `#!cpp std::map`/`#!cpp std::unordered_map` with string keys -- `v` is
   assigned: `#!cpp v = get<T>()`.
+- For a type whose `from_json()` accepts views (see [`get<T>()`](get.md)), that `from_json()` is called with the
+  view and the existing `v`, without building a `BasicJsonType` value.
 - For every other type, the subtree is built into a `BasicJsonType` value and `#!cpp materialize().get_to(v)` is
   called, i.e. `from_json()` is invoked with the existing `v`, exactly as
   [`BasicJsonType::get_to()`](../basic_json/get_to.md) does.

docs/mkdocs/docs/api/basic_json_view/index.md

@@ -64,6 +64,7 @@ still refers to it -- including ones taken before the change -- reads the new va
 
 ## Member types
 
+- **basic_json_type** - `BasicJsonType` (it also marks the class for [`is_json_view`](../is_json_view.md))
 - **value_t** - the JSON type enumeration, see [`basic_json::value_t`](../basic_json/value_t.md)
 - **string_t**, **number_integer_t**, **number_unsigned_t**, **number_float_t**, **json_pointer** - the corresponding
   member types of `BasicJsonType`

docs/mkdocs/docs/api/is_json_view.md

@@ -0,0 +1,55 @@
+# <small>nlohmann::</small>is_json_view
+
+<small>Defined in header `<nlohmann/json_view.hpp>`</small>
+
+```cpp
+template<typename T>
+struct is_json_view;
+```
+
+A type trait: `#!cpp is_json_view<T>::value` is `#!cpp true` if `T` is a [`basic_json_view`](basic_json_view/index.md)
+of any `BasicJsonType` and any [`view_mode`](view_mode.md) -- [`json_view`](json_view.md),
+[`json_editable_view`](json_editable_view.md), [`ordered_json_view`](ordered_json_view.md), ... -- and
+`#!cpp false` otherwise, for [`basic_json`](basic_json/index.md) as well.
+
+It is meant for constraining templates that accept views, in particular a `from_json()` that should read views
+directly: [`get<T>()`](basic_json_view/get.md) on a view calls a `from_json()` with the view only if that `from_json()`
+accepts views but not arbitrary types.
+
+## Template parameters
+
+`T`
+:   the type to check (without cv-qualifiers or references)
+
+## Notes
+
+A view is recognized by its member type `basic_json_type` (a [`basic_json`](basic_json/index.md) specialization) and
+its [`materialize()`](basic_json_view/materialize.md) returning that type, so the trait needs no declaration of the
+view class.
+
+## Examples
+
+??? example
+
+    The example below shows the trait, and a `from_json()` constrained to `json` values and views: `get<T>()` on a view
+    reads the view directly.
+
+    ```cpp
+    --8<-- "examples/is_json_view.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/is_json_view.output"
+    ```
+
+## See also
+
+- [basic_json_view](basic_json_view/index.md) - a handle to one value of a document
+- [get](basic_json_view/get.md) - which conversions read the view directly
+- [view_mode](view_mode.md) - read-only or editable
+
+## Version history
+
+Added in version 3.13.0.

docs/mkdocs/docs/api/macros/index.md

@@ -43,8 +43,6 @@ header. See also the [macro overview page](../../features/macros.md).
 - [**JSON_SKIP_UNSUPPORTED_COMPILER_CHECK**](json_skip_unsupported_compiler_check.md) - do not warn about unsupported compilers
 - [**JSON_USE_GLOBAL_UDLS**](json_use_global_udls.md) - place user-defined string literals (UDLs) into the global namespace
 - [**JSON_USE_SIMDUTF**](json_use_simdutf.md) - use the simdutf library to accelerate UTF-8 validation
-- [**JSON_VIEW_NO_SIMD**](json_view_no_simd.md) - use only portable code in the parser of `json_view.hpp`
-- [**JSON_VIEW_USE_SSSE3**](json_view_use_ssse3.md) - validate non-ASCII strings with SSSE3 in the parser of `json_view.hpp`
 
 ## Library version
 

docs/mkdocs/docs/api/macros/json_no_simd.md

@@ -5,7 +5,8 @@
 ```
 
 When defined, the library uses only portable C++ code where it would otherwise use vector instructions: when scanning
-strings during parsing, and when writing floating-point numbers during serialization.
+strings during parsing, and when writing floating-point numbers during serialization. This includes the parser of
+[`basic_json_document`](../basic_json_document/index.md) (`<nlohmann/json_view.hpp>`).
 
 The macro is an escape hatch, for example for toolchains that cannot compile the vector code, for sanitizers or
 analyzers that do not understand it, or to compare the speed of both variants. It does not change any result: values,
@@ -77,6 +78,7 @@ By default, `#!cpp JSON_NO_SIMD` is not defined, and vector instructions are use
 - [**JSON_USE_SIMDUTF**](json_use_simdutf.md) - use the simdutf library to accelerate UTF-8 validation
 - [**JSON_DISABLE_STREAM_BULK_SCAN**](json_disable_stream_bulk_scan.md) - read a `std::istream` one character at a time
 - [Parsing: input sources and performance](../../features/parsing/index.md#input-sources-and-performance)
+- [json_view](../../features/json_view.md) - the zero-copy view, whose parser the macro also affects
 
 ## Version history
 

docs/mkdocs/docs/api/macros/json_view_no_simd.md

@@ -1,52 +0,0 @@
-# JSON_VIEW_NO_SIMD
-
-```cpp
-#define JSON_VIEW_NO_SIMD
-```
-
-When defined, the parser of [`basic_json_document`](../basic_json_document/index.md) (`<nlohmann/json_view.hpp>`)
-uses only portable C++ to scan strings. By default, it scans long runs of string bytes 16 at a time with NEON on
-AArch64 (with GCC and Clang) and SSE2 on x86-64, which are part of the baseline instruction sets of these
-architectures, and validates non-ASCII text with NEON (or SSSE3, see
-[`JSON_VIEW_USE_SSSE3`](json_view_use_ssse3.md)).
-
-The same input is accepted or rejected either way, with the same values, and errors are reported the same way; only
-the speed differs. The macro exists for platforms whose compilers lack the intrinsics headers, and to test the portable
-code.
-
-!!! note "ABI compatibility"
-
-    The macro selects between two definitions of the same inline functions. Whether it is defined is encoded in the
-    [namespace](../../features/namespace.md) (tag `_vns`), resulting in distinct symbol names. Translation units
-    compiled with and without it can therefore be linked into the same program without One Definition Rule (ODR)
-    violations, but they cannot exchange instances of library types.
-
-## Default definition
-
-By default, `#!cpp JSON_VIEW_NO_SIMD` is not defined, and the vector code is used where available.
-
-```cpp
-#undef JSON_VIEW_NO_SIMD
-```
-
-## Examples
-
-??? example
-
-    The code below uses the portable string scanning of the view.
-
-    ```cpp
-    #define JSON_VIEW_NO_SIMD
-    #include <nlohmann/json_view.hpp>
-
-    ...
-    ```
-
-## See also
-
-- [JSON_VIEW_USE_SSSE3](json_view_use_ssse3.md) - validate non-ASCII strings with SSSE3 on x86-64
-- [json_view](../../features/json_view.md) - the zero-copy view
-
-## Version history
-
-- Added in version 3.13.0.

docs/mkdocs/docs/api/macros/json_view_use_ssse3.md

@@ -1,53 +0,0 @@
-# JSON_VIEW_USE_SSSE3
-
-```cpp
-#define JSON_VIEW_USE_SSSE3
-```
-
-When defined on x86-64, the parser of [`basic_json_document`](../basic_json_document/index.md)
-(`<nlohmann/json_view.hpp>`) validates non-ASCII text in strings with SSSE3 without asking the CPU first.
-
-By default, the parser checks once at run time whether the CPU has SSSE3 (all x86-64 CPUs since about 2011 have it)
-and then validates non-ASCII text 16 bytes at a time, using the "lookup4" algorithm of
-[simdjson](https://github.com/simdjson/simdjson); on CPUs without SSSE3, it validates one UTF-8 sequence at a time.
-The vector check is compiled for SSSE3 with a function attribute (GCC 4.9 and later, Clang), so this needs no compiler
-option. With MSVC, the check uses `__cpuid`. On AArch64, the vector check uses NEON and is always on.
-
-Define the macro only together with a compiler option that enables SSSE3 (e.g. `-mssse3`, or `-march=` with a CPU that
-has it), and only for programs that run on such CPUs. It saves the check of the CPU, which costs little. The same
-input is accepted or rejected either way; only the speed of non-ASCII text differs.
-
-!!! note "ABI compatibility"
-
-    The macro selects between two definitions of the same inline functions. Whether it is defined is encoded in the
-    [namespace](../../features/namespace.md) (tag `_vssse3`, on every architecture), resulting in distinct symbol
-    names. Translation units compiled with and without it can therefore be linked into the same program without One
-    Definition Rule (ODR) violations, but they cannot exchange instances of library types.
-
-## Default definition
-
-By default, `#!cpp JSON_VIEW_USE_SSSE3` is not defined.
-
-```cpp
-#undef JSON_VIEW_USE_SSSE3
-```
-
-## Examples
-
-??? example
-
-    With CMake, for a program that only runs on CPUs with SSSE3:
-
-    ```cmake
-    target_compile_definitions(your_target PRIVATE JSON_VIEW_USE_SSSE3)
-    target_compile_options(your_target PRIVATE -mssse3)
-    ```
-
-## See also
-
-- [JSON_VIEW_NO_SIMD](json_view_no_simd.md) - use only portable code in the view's parser
-- [JSON_USE_SIMDUTF](json_use_simdutf.md) - validate UTF-8 with simdutf in `basic_json`'s parser
-
-## Version history
-
-- Added in version 3.13.0.

docs/mkdocs/docs/api/macros/nlohmann_define_derived_type.md

@@ -147,6 +147,13 @@ void to_json(BasicJsonType& j, const B& b) {
     See Implementation limits for [NLOHMANN_DEFINE_TYPE_INTRUSIVE](nlohmann_define_type_intrusive.md) and
     [NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE](nlohmann_define_type_non_intrusive.md), respectively.
 
+!!! info "Views"
+
+    The generated `from_json()` also reads the views of [`json_document`](../json_document.md)s
+    (`<nlohmann/json_view.hpp>`): [`get<T>()`](../basic_json_view/get.md) on a view looks the members up in the
+    view, without building a `json` value first. The base part is read from the view as well if the base's
+    `from_json()` accepts views, and from [`materialize()`](../basic_json_view/materialize.md) otherwise.
+
 ## Examples
 
 ??? example "Example: (1) NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE"
@@ -192,3 +199,5 @@ void to_json(BasicJsonType& j, const B& b) {
 6. Added in version 3.12.0.
 
 All six macros were changed to allow an empty member list in version 3.13.0.
+
+The generated `from_json()` reads the views of `json_document`s since version 3.13.0.

docs/mkdocs/docs/api/macros/nlohmann_define_type_intrusive.md

@@ -81,6 +81,12 @@ See the examples below for the concrete generated code.
       that serializes a struct's members positionally into a JSON array; for that, write `to_json`/`from_json` by
       hand, building/reading a `json::array()` of the members in order.
 
+!!! info "Views"
+
+    The generated `from_json()` also reads the views of [`json_document`](../json_document.md)s
+    (`<nlohmann/json_view.hpp>`): [`get<T>()`](../basic_json_view/get.md) on a view looks the members up in the
+    view, without building a `json` value first.
+
 ## Examples
 
 ??? example "Example: (1) NLOHMANN_DEFINE_TYPE_INTRUSIVE"
@@ -189,3 +195,5 @@ See the examples below for the concrete generated code.
 
 All three macros were changed to work with any `basic_json` specialization (not only `nlohmann::json`) in version 3.12.0,
 and to allow an empty member list in version 3.13.0.
+
+The generated `from_json()` reads the views of `json_document`s since version 3.13.0.

docs/mkdocs/docs/api/macros/nlohmann_define_type_non_intrusive.md

@@ -80,6 +80,12 @@ See the examples below for the concrete generated code.
       that serializes a struct's members positionally into a JSON array; for that, write `to_json`/`from_json` by
       hand, building/reading a `json::array()` of the members in order.
 
+!!! info "Views"
+
+    The generated `from_json()` also reads the views of [`json_document`](../json_document.md)s
+    (`<nlohmann/json_view.hpp>`): [`get<T>()`](../basic_json_view/get.md) on a view looks the members up in the
+    view, without building a `json` value first.
+
 ## Examples
 
 ??? example "Example: (1) NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE"
@@ -188,3 +194,5 @@ See the examples below for the concrete generated code.
 
 All three macros were changed to work with any `basic_json` specialization (not only `nlohmann::json`) in version 3.12.0,
 and to allow an empty member list in version 3.13.0.
+
+The generated `from_json()` reads the views of `json_document`s since version 3.13.0.

docs/mkdocs/docs/api/macros/nlohmann_json_namespace.md

@@ -39,6 +39,6 @@ the library.
 ## Version history
 
 - Added in version 3.11.0. Changed inline namespace name in version 3.11.2. Added the ABI tag `_dp` in
-  version 3.12.0, and the ABI tags `_bics`, `_psp`, `_snul`, `_sbu8`, `_ekmo`, `_dsbs`, `_dufio`, `_ns`, `_vns`,
+  version 3.12.0, and the ABI tags `_bics`, `_psp`, `_snul`, `_sbu8`, `_ekmo`, `_dsbs`, `_dufio`, and `_ns` in
-  and `_vssse3` in version 3.13.0; see
+  version 3.13.0; see
   [`nlohmann` Namespace](../../features/namespace.md#structure).

docs/mkdocs/docs/api/macros/nlohmann_json_serialize_enum.md

@@ -45,6 +45,12 @@ inline void from_json(const BasicJsonType& j, type& e);
       Define [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md) to store them as objects
       with the converted keys. Such maps can be read from both forms.
 
+!!! info "Views"
+
+    The generated `from_json()` also reads the views of [`json_document`](../json_document.md)s
+    (`<nlohmann/json_view.hpp>`), comparing the view with the entries of the mapping, without building a `json` value
+    first.
+
 ## Examples
 
 ??? example "Example: Basic usage"
@@ -88,3 +94,5 @@ inline void from_json(const BasicJsonType& j, type& e);
 ## Version history
 
 Added in version 3.4.0.
+
+The generated `from_json()` reads the views of `json_document`s since version 3.13.0.

docs/mkdocs/docs/api/macros/nlohmann_json_serialize_enum_strict.md

@@ -48,6 +48,12 @@ inline void from_json(const BasicJsonType& j, type& e);
       Define [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md) to store them as objects
       with the converted keys. Such maps can be read from both forms.
 
+!!! info "Views"
+
+    The generated `from_json()` also reads the views of [`json_document`](../json_document.md)s
+    (`<nlohmann/json_view.hpp>`), comparing the view with the entries of the mapping, without building a `json` value
+    first.
+
 ## Examples
 
 ??? example "Example: Basic usage"

docs/mkdocs/docs/examples/is_json_view.cpp

@@ -0,0 +1,34 @@
+#include <iostream>
+#include <type_traits>
+#include <nlohmann/json_view.hpp>
+
+using nlohmann::json;
+
+namespace ns
+{
+struct person
+{
+    std::string name;
+    int age = 0;
+};
+
+// reads json values and views (of any document type), but nothing else
+template < typename J, typename std::enable_if < nlohmann::is_json_view<J>::value || std::is_same<J, json>::value, int >::type = 0 >
+void from_json(const J& j, person& p)
+{
+    p.name = j.at("name").template get<std::string>();
+    p.age = j.at("age").template get<int>();
+}
+} // namespace ns
+
+int main()
+{
+    std::cout << std::boolalpha
+              << nlohmann::is_json_view<nlohmann::json_view>::value << ' '
+              << nlohmann::is_json_view<nlohmann::ordered_json_editable_view>::value << ' '
+              << nlohmann::is_json_view<json>::value << '\n';
+
+    const nlohmann::json_document doc = nlohmann::json_document::parse(R"({"name": "Ada", "age": 36})");
+    const auto p = doc.root().get<ns::person>(); // reads the view, no json value is built
+    std::cout << p.name << ' ' << p.age << '\n';
+}

docs/mkdocs/docs/examples/is_json_view.output

@@ -0,0 +1,2 @@
+true true false
+Ada 36

docs/mkdocs/docs/features/json_view.md

@@ -185,6 +185,10 @@ key as well. Other zero-copy parsers that index the source text, such as yyjson
 member. RFC 8259 only says that names within an object SHOULD be unique and that the behavior of a receiver that sees
 duplicates is unpredictable, so neither choice is wrong.
 
+The same holds for [`get<T>()`](../api/basic_json_view/get.md) of a type whose `from_json()` reads the view, such as
+the types of the `NLOHMANN_DEFINE_TYPE_*` macros: their members are looked up, so `#!cpp get<point>()` of
+`#!cpp {"x":1,"x":2}` reads `#!cpp x == 1`, while `#!cpp materialize().get<point>()` reads `#!cpp 2`.
+
 **What stays the same as `parse()`?** [`materialize()`](../api/basic_json_view/materialize.md) and
 [`get<std::map<...>>()`](../api/basic_json_view/get.md) replay every member in order, so they keep the *last* value
 exactly like `#!cpp basic_json::parse()` (at the position of the first occurrence of the key, for an
@@ -354,9 +358,10 @@ validation entirely, for an image trusted as much as the process's own memory. S
 !!! warning "Experimental"
 
     The image format is versioned but not yet stable, and may change in an incompatible way before it is declared
-    stable. It is little-endian only, and tied to the library build that wrote it -- use it to cache a document or to
+    stable. It is little-endian only (on big-endian targets, `save()` and `load()` do not exist), and tied to the
-    hand one to another process running the *same* build, not as a long-term storage format; keep the original JSON
+    library build that wrote it -- use it to cache a document or to hand one to another process running the *same*
-    text if a saved document needs to be readable by a future library version.
+    build, not as a long-term storage format; keep the original JSON text if a saved document needs to be readable by
+    a future library version.
 
 The idea of a document you can read without parsing comes from zero-copy formats such as
 [FlatBuffers](https://github.com/google/flatbuffers) and [YaFF](https://github.com/yandex/yaff); the check

docs/mkdocs/docs/features/macros.md

@@ -287,23 +287,6 @@ external dependency and is not defined by default.
 
 See [full documentation of `JSON_USE_SIMDUTF`](../api/macros/json_use_simdutf.md).
 
-## `JSON_VIEW_NO_SIMD`
-
-When defined, the parser of [`basic_json_document`](../api/basic_json_document/index.md)
-(`<nlohmann/json_view.hpp>`) uses only portable C++ to scan strings, instead of vector instructions (SSE2 on x86-64,
-NEON on AArch64). The same input is accepted or rejected either way; only the speed differs. It is not defined by
-default.
-
-See [full documentation of `JSON_VIEW_NO_SIMD`](../api/macros/json_view_no_simd.md).
-
-## `JSON_VIEW_USE_SSSE3`
-
-When defined on x86-64, the parser of [`basic_json_document`](../api/basic_json_document/index.md)
-(`<nlohmann/json_view.hpp>`) validates non-ASCII text in strings with SSSE3 without asking the CPU first. It is not
-defined by default.
-
-See [full documentation of `JSON_VIEW_USE_SSSE3`](../api/macros/json_view_use_ssse3.md).
-
 ## `NLOHMANN_DEFINE_TYPE_*(...)`, `NLOHMANN_DEFINE_DERIVED_TYPE_*(...)`
 
 The library defines 12 macros to simplify the serialization/deserialization of types. See the page on

docs/mkdocs/docs/features/namespace.md

@@ -28,8 +28,6 @@ The complete default namespace name is derived as follows:
     - [`JSON_DISABLE_UNLOCKED_FILE_IO`](../api/macros/json_disable_unlocked_file_io.md) defined non-zero appends
       `_dufio`.
     - [`JSON_NO_SIMD`](../api/macros/json_no_simd.md) defined appends `_ns`.
-    - [`JSON_VIEW_NO_SIMD`](../api/macros/json_view_no_simd.md) defined appends `_vns`.
-    - [`JSON_VIEW_USE_SSSE3`](../api/macros/json_view_use_ssse3.md) defined appends `_vssse3`.
 - The inline namespace ends with the suffix `_v` followed by the 3 components of the version number separated by
   underscores. To omit the version component, see [Disabling the version component](#disabling-the-version-component)
   below.
@@ -115,7 +113,5 @@ follows:
   ([`JSON_STRICT_BINARY_UTF8`](../api/macros/json_strict_binary_utf8.md)), `_ekmo`
   ([`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](../api/macros/json_use_objects_for_enum_keyed_maps.md)), `_dsbs`
   ([`JSON_DISABLE_STREAM_BULK_SCAN`](../api/macros/json_disable_stream_bulk_scan.md)), `_dufio`
-  ([`JSON_DISABLE_UNLOCKED_FILE_IO`](../api/macros/json_disable_unlocked_file_io.md)), `_ns`
+  ([`JSON_DISABLE_UNLOCKED_FILE_IO`](../api/macros/json_disable_unlocked_file_io.md)), and `_ns`
-  ([`JSON_NO_SIMD`](../api/macros/json_no_simd.md)), `_vns`
+  ([`JSON_NO_SIMD`](../api/macros/json_no_simd.md)) in version 3.13.0.
-  ([`JSON_VIEW_NO_SIMD`](../api/macros/json_view_no_simd.md)), and `_vssse3`
-  ([`JSON_VIEW_USE_SSSE3`](../api/macros/json_view_use_ssse3.md)) in version 3.13.0.

docs/mkdocs/docs/home/debugging.md

@@ -21,10 +21,10 @@ ABI tags are not covered and may show raw internal fields instead. To generate a
     ```
 
 3. Generate a Natvis file with the tags of your configuration, for example for `JSON_DIAGNOSTICS`,
-    `JSON_DIAGNOSTIC_POSITIONS`, and `JSON_VIEW_NO_SIMD`:
+    `JSON_DIAGNOSTIC_POSITIONS`, and `JSON_NO_SIMD`:
 
     ```shell
-    make natvis NATVIS_ARGS="--abi-tags _diag,_dp,_vns --output my_nlohmann_json.natvis"
+    make natvis NATVIS_ARGS="--abi-tags _diag,_dp,_ns --output my_nlohmann_json.natvis"
     ```
 
 4. Use the generated file instead of `nlohmann_json.natvis`.

docs/mkdocs/docs/home/exceptions.md

@@ -853,17 +853,12 @@ from JSON text.
 
 [`basic_json_document::save()`](../api/basic_json_document/save.md) cannot write an
 [image](../features/json_view.md#images) of a [discarded](../api/basic_json_document/is_discarded.md) document.
-[`save()`](../api/basic_json_document/save.md) and [`load()`](../api/basic_json_document/load.md) also throw this
-exception on a big-endian target, since the image format is little-endian only.
 
 !!! failure "Example messages"
 
     ```
     [json.exception.type_error.320] cannot save a discarded json_document
     ```
-    ```
-    [json.exception.type_error.320] json_document images need a little-endian target
-    ```
 
 !!! note
 

docs/mkdocs/mkdocs.yml

@@ -358,6 +358,7 @@ nav:
           - 'Overview': api/adl_serializer/index.md
           - 'from_json': api/adl_serializer/from_json.md
           - 'to_json': api/adl_serializer/to_json.md
+      - 'is_json_view': api/is_json_view.md
       - 'json': api/json.md
       - 'json_document': api/json_document.md
       - 'json_editable_document': api/json_editable_document.md
@@ -442,8 +443,6 @@ nav:
           - 'JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON': api/macros/json_use_legacy_discarded_value_comparison.md
           - 'JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS': api/macros/json_use_objects_for_enum_keyed_maps.md
           - 'JSON_USE_SIMDUTF': api/macros/json_use_simdutf.md
-          - 'JSON_VIEW_NO_SIMD': api/macros/json_view_no_simd.md
-          - 'JSON_VIEW_USE_SSSE3': api/macros/json_view_use_ssse3.md
           - 'NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_derived_type.md
           - 'NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_type_intrusive.md
           - 'NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_type_non_intrusive.md

include/nlohmann/detail/abi_macros.hpp

@@ -128,26 +128,14 @@
     #define NLOHMANN_JSON_ABI_TAG_NO_SIMD
 #endif
 
-#ifdef JSON_VIEW_NO_SIMD
-    #define NLOHMANN_JSON_ABI_TAG_VIEW_NO_SIMD _vns
-#else
-    #define NLOHMANN_JSON_ABI_TAG_VIEW_NO_SIMD
-#endif
-
-#ifdef JSON_VIEW_USE_SSSE3
-    #define NLOHMANN_JSON_ABI_TAG_VIEW_USE_SSSE3 _vssse3
-#else
-    #define NLOHMANN_JSON_ABI_TAG_VIEW_USE_SSSE3
-#endif
-
 #ifndef NLOHMANN_JSON_NAMESPACE_NO_VERSION
     #define NLOHMANN_JSON_NAMESPACE_NO_VERSION 0
 #endif
 
 // Construct the namespace ABI tags component
-#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g, h, i, j, k, l, m) json_abi ## a ## b ## c ## d ## e ## f ## g ## h ## i ## j ## k ## l ## m
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g, h, i, j, k) json_abi ## a ## b ## c ## d ## e ## f ## g ## h ## i ## j ## k
-#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f, g, h, i, j, k, l, m) \
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f, g, h, i, j, k) \
-    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g, h, i, j, k, l, m)
+    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g, h, i, j, k)
 
 #define NLOHMANN_JSON_ABI_TAGS                                       \
     NLOHMANN_JSON_ABI_TAGS_CONCAT(                                   \
@@ -161,9 +149,7 @@
             NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS,       \
             NLOHMANN_JSON_ABI_TAG_DISABLE_STREAM_BULK_SCAN,          \
             NLOHMANN_JSON_ABI_TAG_DISABLE_UNLOCKED_FILE_IO,          \
-            NLOHMANN_JSON_ABI_TAG_NO_SIMD,                           \
+            NLOHMANN_JSON_ABI_TAG_NO_SIMD)
-            NLOHMANN_JSON_ABI_TAG_VIEW_NO_SIMD,                      \
-            NLOHMANN_JSON_ABI_TAG_VIEW_USE_SSSE3)
 
 // Construct the namespace version component
 #define NLOHMANN_JSON_NAMESPACE_VERSION_CONCAT_EX(major, minor, patch) \

include/nlohmann/detail/conversions/from_json.hpp

@@ -10,6 +10,7 @@
 
 #include <algorithm> // min, transform
 #include <array> // array
+#include <cstddef> // nullptr_t
 #include <forward_list> // forward_list
 #include <iterator> // inserter, front_inserter, end
 #include <map> // map
@@ -27,6 +28,7 @@
 #include <nlohmann/detail/meta/identity_tag.hpp>
 #include <nlohmann/detail/meta/std_fs.hpp>
 #include <nlohmann/detail/meta/type_traits.hpp>
+#include <nlohmann/detail/output/error_handler.hpp>
 #include <nlohmann/detail/string_concat.hpp>
 #include <nlohmann/detail/value_t.hpp>
 
@@ -665,16 +667,114 @@ inline void from_json(const BasicJsonType& j, std_fs::path& p)
 }
 #endif
 
-struct from_json_fn
+namespace from_json_adl
 {
-    template<typename BasicJsonType, typename T>
+// hides the library's from_json() overloads above (and the from_json object):
-    auto operator()(const BasicJsonType& j, T&& val) const
+// a call from this namespace finds only the from_json() functions of the
+// arguments' own namespaces and classes (ADL); the declaration is never viable
+// and never defined (not "= delete", which GCC before 6 reports as a use)
+struct hidden;
+void from_json(const hidden&);
+
+// a type no from_json() written for JSON values accepts: a from_json() that
+// accepts it is not constrained to them (see has_view_from_json; it lives
+// here, so that ADL finds no other from_json() for it)
+struct probe
+{};
+
+struct fn
+{
+    template<typename SourceType, typename T>
+    auto operator()(const SourceType& j, T&& val) const
     noexcept(noexcept(from_json(j, std::forward<T>(val))))
     -> decltype(from_json(j, std::forward<T>(val)))
     {
         return from_json(j, std::forward<T>(val));
     }
 };
+}  // namespace from_json_adl
+
+// the sources whose from_json() is only looked up by ADL: views (the library's
+// overloads are written for basic_json) and the probe
+template<typename T>
+struct is_adl_only_from_json_source : disjunction<is_json_view<T>, std::is_same<T, from_json_adl::probe>> {};
+
+struct from_json_fn
+{
+    template < typename BasicJsonType, typename T,
+               enable_if_t < !is_adl_only_from_json_source<BasicJsonType>::value, int > = 0 >
+    auto operator()(const BasicJsonType& j, T && val) const
+    noexcept(noexcept(from_json(j, std::forward<T>(val))))
+    -> decltype(from_json(j, std::forward<T>(val)))
+    {
+        return from_json(j, std::forward<T>(val));
+    }
+
+    template < typename SourceType, typename T,
+               enable_if_t < is_adl_only_from_json_source<SourceType>::value, int > = 0 >
+    auto operator()(const SourceType& j, T && val) const
+    noexcept(noexcept(from_json_adl::fn {}(j, std::forward<T>(val))))
+    -> decltype(from_json_adl::fn {}(j, std::forward<T>(val)))
+    {
+        return from_json_adl::fn {}(j, std::forward<T>(val));
+    }
+};
+
+// Whether JSONSerializer::from_json(view, T&) reads T from a view (of
+// <nlohmann/json_view.hpp>) directly: it must accept the view but not the
+// probe. An unconstrained from_json() template (written for basic_json, but
+// accepting anything) is thus not called with a view, nor are the library's
+// own conversions; the view converts such types through materialize().
+template<typename Serializer, typename SourceType, typename T>
+using serializer_from_json_t = decltype(Serializer::from_json(std::declval<const SourceType&>(), std::declval<T&>()));
+
+template<typename Serializer, typename View, typename T>
+struct has_view_from_json
+    : conjunction < is_detected<serializer_from_json_t, Serializer, View, T>,
+      negation<is_detected<serializer_from_json_t, Serializer, from_json_adl::probe, T>>> {};
+
+// the base part of a type of the NLOHMANN_DEFINE_DERIVED_TYPE_* macros: from a
+// view through its get_to(), which reads the base from the view where the
+// base's from_json() accepts views, and from materialize() otherwise
+template<typename BasicJsonType, typename T, enable_if_t<is_basic_json<BasicJsonType>::value, int> = 0>
+void from_json_base(const BasicJsonType& j, T& base)
+{
+    from_json_fn {}(j, base);
+}
+
+template<typename View, typename T, enable_if_t<is_json_view<View>::value, int> = 0>
+void from_json_base(const View& v, T& base)
+{
+    v.get_to(base);
+}
+
+// the context of an exception thrown by a from_json() of the macros: the value
+// itself for basic_json (for JSON_DIAGNOSTICS), none for a view
+template<typename BasicJsonType, enable_if_t<is_basic_json<BasicJsonType>::value, int> = 0>
+const BasicJsonType * from_json_context(const BasicJsonType& j) noexcept
+{
+    return &j;
+}
+
+template<typename View, enable_if_t<is_json_view<View>::value, int> = 0>
+std::nullptr_t from_json_context(const View& /*unused*/) noexcept
+{
+    return nullptr;
+}
+
+// a value as an exception message shows it (invalid UTF-8 replaced; the
+// strings of a view are always valid UTF-8)
+template<typename BasicJsonType, enable_if_t<is_basic_json<BasicJsonType>::value, int> = 0>
+typename BasicJsonType::string_t from_json_dump(const BasicJsonType& j)
+{
+    return j.dump(-1, ' ', false, error_handler_t::replace);
+}
+
+template<typename View, enable_if_t<is_json_view<View>::value, int> = 0>
+typename View::string_t from_json_dump(const View& v)
+{
+    return v.dump();
+}
 
 }  // namespace detail
 

include/nlohmann/detail/exceptions.hpp

@@ -102,7 +102,7 @@ enum class exception_id : int
     type_not_serializable = 317, ///< a value cannot be serialized to the requested binary format
     enum_key_duplicate = 318, ///< an enum-keyed map has two keys that serialize to the same string
     document_binary_value = 319, ///< a binary value is stored in a json_document
-    document_image_unsupported = 320, ///< a json_document image cannot be saved or loaded (discarded document, big-endian target)
+    document_image_unsupported = 320, ///< a discarded json_document cannot be saved as an image
     discarded_value_used = 321, ///< a discarded value is used
     // out_of_range
     array_index_out_of_range = 401, ///< an array index is out of range

include/nlohmann/detail/macro_scope.hpp

@@ -291,15 +291,17 @@
         });                                                                                     \
         j = ((it != std::end(m)) ? it : std::begin(m))->second;                                 \
     }                                                                                           \
-    template<typename BasicJsonType>                                                            \
+    template<typename BasicJsonType, nlohmann::detail::enable_if_t<nlohmann::detail::is_basic_json_or_view<BasicJsonType>::value, int> = 0> \
     inline void from_json(const BasicJsonType& j, ENUM_TYPE& e)                                 \
     {                                                                                           \
         /* NOLINTNEXTLINE(modernize-type-traits) we use C++11 */                                \
         static_assert(std::is_enum<ENUM_TYPE>::value, #ENUM_TYPE " must be an enum!");          \
+        /* (for a view, the table holds basic_json values, which compare with the view) */      \
+        using nlohmann_json_value_t = nlohmann::detail::json_type_of_t<BasicJsonType>;          \
         /* NOLINTNEXTLINE(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) we don't want to depend on <array> */ \
-        static const std::pair<ENUM_TYPE, BasicJsonType> m[] = __VA_ARGS__;                     \
+        static const std::pair<ENUM_TYPE, nlohmann_json_value_t> m[] = __VA_ARGS__;             \
         auto it = std::find_if(std::begin(m), std::end(m),                                      \
-                               [&j](const std::pair<ENUM_TYPE, BasicJsonType>& ej_pair) -> bool \
+                               [&j](const std::pair<ENUM_TYPE, nlohmann_json_value_t>& ej_pair) -> bool \
         {                                                                                       \
             return ej_pair.second == j;                                                         \
         });                                                                                     \
@@ -330,20 +332,22 @@
         if (it != std::end(m)) j = it->second;                                                  \
         else ::nlohmann::detail::templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(nlohmann::detail::exception_id::value_out_of_range,"enum value out of range for " #ENUM_TYPE, nullptr)); \
     }                                                                                           \
-    template<typename BasicJsonType>                                                            \
+    template<typename BasicJsonType, nlohmann::detail::enable_if_t<nlohmann::detail::is_basic_json_or_view<BasicJsonType>::value, int> = 0> \
     inline void from_json(const BasicJsonType& j, ENUM_TYPE& e)                                 \
     {                                                                                           \
         /* NOLINTNEXTLINE(modernize-type-traits) we use C++11 */                                \
         static_assert(std::is_enum<ENUM_TYPE>::value, #ENUM_TYPE " must be an enum!");          \
+        /* (for a view, the table holds basic_json values, which compare with the view) */      \
+        using nlohmann_json_value_t = nlohmann::detail::json_type_of_t<BasicJsonType>;          \
         /* NOLINTNEXTLINE(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) we don't want to depend on <array> */ \
-        static const std::pair<ENUM_TYPE, BasicJsonType> m[] = __VA_ARGS__;                     \
+        static const std::pair<ENUM_TYPE, nlohmann_json_value_t> m[] = __VA_ARGS__;             \
         auto it = std::find_if(std::begin(m), std::end(m),                                      \
-                               [&j](const std::pair<ENUM_TYPE, BasicJsonType>& ej_pair) -> bool \
+                               [&j](const std::pair<ENUM_TYPE, nlohmann_json_value_t>& ej_pair) -> bool \
         {                                                                                       \
             return ej_pair.second == j;                                                         \
         });                                                                                     \
         if (it != std::end(m)) e = it->first;                                                   \
-        else ::nlohmann::detail::templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(nlohmann::detail::exception_id::value_out_of_range, nlohmann::detail::concat("enum value out of range for " #ENUM_TYPE ": ", j.dump(-1, ' ', false, nlohmann::detail::error_handler_t::replace)), &j)); \
+        else ::nlohmann::detail::templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(nlohmann::detail::exception_id::value_out_of_range, nlohmann::detail::concat("enum value out of range for " #ENUM_TYPE ": ", nlohmann::detail::from_json_dump(j)), nlohmann::detail::from_json_context(j))); \
     }
 
 // Ugly macros to avoid uglier copy-paste when specializing basic_json. They
@@ -603,6 +607,8 @@
 #define NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME(v1, v2) nlohmann_json_t.v2 = !nlohmann_json_j.is_null() ? nlohmann_json_j.value(v1, nlohmann_json_default_obj.v2) : nlohmann_json_default_obj.v2;
 
 #define NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(...) template<typename BasicJsonType, nlohmann::detail::enable_if_t<nlohmann::detail::is_basic_json<BasicJsonType>::value, int> = 0> __VA_ARGS__
+// from_json() also reads from the views of <nlohmann/json_view.hpp>
+#define NLOHMANN_JSON_FROM_TYPE_TEMPLATE(...) template<typename BasicJsonType, nlohmann::detail::enable_if_t<nlohmann::detail::is_basic_json_or_view<BasicJsonType>::value, int> = 0> __VA_ARGS__
 
 // Helpers used to dispatch the NLOHMANN_DEFINE_TYPE_*/NLOHMANN_DEFINE_DERIVED_TYPE_*
 // macros below between a zero-member and a one-or-more-member implementation
@@ -655,18 +661,18 @@
 */
 #define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_MEMBERS(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
 #define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_EMPTY(Type)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); }) \
     /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type is used as a declarator type, not in an expression */ \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType&, Type&) noexcept { })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType&, Type&) noexcept { })
 
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_TYPE_BODY(NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_, __VA_ARGS__)(__VA_ARGS__))
 
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
 
 /*!
 @brief macro
@@ -676,7 +682,7 @@
 */
 #define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_MEMBERS(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
 // identical to NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_EMPTY: with no members there is nothing to default
 #define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_EMPTY(Type) NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_EMPTY(Type)
@@ -685,7 +691,7 @@
 
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
 
 /*!
 @brief macro
@@ -712,18 +718,18 @@
 */
 #define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_MEMBERS(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
 #define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_EMPTY(Type)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); }) \
     /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type is used as a declarator type, not in an expression */ \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType&, Type&) noexcept { })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType&, Type&) noexcept { })
 
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_TYPE_BODY(NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_, __VA_ARGS__)(__VA_ARGS__))
 
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
 
 /*!
 @brief macro
@@ -733,7 +739,7 @@
 */
 #define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_MEMBERS(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
 // identical to NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_EMPTY: with no members there is nothing to default
 #define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_EMPTY(Type) NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_EMPTY(Type)
@@ -742,7 +748,7 @@
 
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
 
 /*!
 @brief macro
@@ -769,18 +775,18 @@
 */
 #define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_MEMBERS(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
 #define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_EMPTY(Type, BaseType)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); }) \
     /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type/BaseType are used as declarator types, not in expressions */ \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
 
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DERIVED_TYPE_BODY(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_, __VA_ARGS__)(__VA_ARGS__))
 
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
 
 /*!
 @brief macro
@@ -790,7 +796,7 @@
 */
 #define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_MEMBERS(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
 // identical to NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_EMPTY: with no members there is nothing to default
 #define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_EMPTY(Type, BaseType) NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_EMPTY(Type, BaseType)
@@ -799,7 +805,7 @@
 
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
 
 /*!
 @brief macro
@@ -827,18 +833,18 @@
 */
 #define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_MEMBERS(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
 #define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_EMPTY(Type, BaseType)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); }) \
     /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type/BaseType are used as declarator types, not in expressions */ \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
 
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DERIVED_TYPE_BODY(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_, __VA_ARGS__)(__VA_ARGS__))
 
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
 
 /*!
 @brief macro
@@ -848,7 +854,7 @@
 */
 #define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_MEMBERS(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
 // identical to NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_EMPTY: with no members there is nothing to default
 #define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_EMPTY(Type, BaseType) NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_EMPTY(Type, BaseType)
@@ -857,7 +863,7 @@
 
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
 
 /*!
 @brief macro

include/nlohmann/detail/meta/type_traits.hpp

@@ -340,6 +340,47 @@ template<class B> struct negation : std::integral_constant < bool, !B::value > {
 
 #endif
 
+///////////////////////
+// json_view helpers //
+///////////////////////
+
+template<typename T>
+using basic_json_type_t = typename T::basic_json_type;
+
+template<typename T>
+using materialize_function_t = decltype(std::declval<const T&>().materialize());
+
+// a basic_json_view of <nlohmann/json_view.hpp> (detected by its member type
+// basic_json_type, a basic_json, and materialize() returning that type, so that
+// json.hpp needs no declaration of the view)
+template<typename T, typename = void>
+struct is_json_view : std::false_type {};
+
+template<typename T>
+struct is_json_view<T, enable_if_t<is_basic_json<detected_t<basic_json_type_t, T>>::value>>
+    : std::is_same<detected_t<materialize_function_t, T>, basic_json_type_t<T>> {};
+
+// the types from_json() functions of the NLOHMANN_DEFINE_TYPE_* and
+// NLOHMANN_JSON_SERIALIZE_ENUM macros read from
+template<typename T>
+struct is_basic_json_or_view : disjunction<is_basic_json<T>, is_json_view<T>> {};
+
+// the basic_json type of a basic_json value or of a view
+template<typename T, typename = void>
+struct json_type_of
+{
+    using type = T;
+};
+
+template<typename T>
+struct json_type_of<T, enable_if_t<is_json_view<T>::value>>
+{
+    using type = typename T::basic_json_type;
+};
+
+template<typename T>
+using json_type_of_t = typename json_type_of<T>::type;
+
 // Reimplementation of is_constructible and is_default_constructible, due to them being broken for
 // std::pair and std::tuple until LWG 2367 fix (see https://cplusplus.github.io/LWG/lwg-defects.html#2367).
 // This causes compile errors in e.g., Clang 3.5 or GCC 4.9.

include/nlohmann/detail/view/image.hpp

@@ -182,12 +182,10 @@ inline void compact_nodes(const document_data& d, std::size_t arena_size, std::v
     }
 }
 
+#if NLOHMANN_VIEW_LITTLE_ENDIAN // (the image format is little-endian: no save() elsewhere)
 /// the document as an image
 inline std::vector<std::uint8_t> save_image(const document_data& d)
 {
-#if !NLOHMANN_VIEW_LITTLE_ENDIAN
-    throw_type_error(exception_id::document_image_unsupported, "json_document images need a little-endian target"); // LCOV_EXCL_LINE
-#endif
     const std::size_t arena_size = d.arena_size;
     std::vector<node> compacted;
     std::string text_tail;
@@ -243,6 +241,7 @@ inline std::vector<std::uint8_t> save_image(const document_data& d)
     *o = 0;
     return image;
 }
+#endif
 
 /// the parts of a number token that the checks need
 struct number_token
@@ -663,13 +662,11 @@ inline bool check_image(const node* nodes, std::size_t count, const unsigned cha
     throw_parse_error(exception_id::invalid_document_image, concat("invalid json_document image: ", what));
 }
 
+#if NLOHMANN_VIEW_LITTLE_ENDIAN // (the image format is little-endian: no load() elsewhere)
 /// Read an image into d. The text and the decoded strings stay in the image;
 /// the nodes are copied (so that they are aligned, and edits can change them).
 inline void load_image(document_data& d, const std::uint8_t* image, std::size_t size, image_check check)
 {
-#if !NLOHMANN_VIEW_LITTLE_ENDIAN
-    throw_type_error(exception_id::document_image_unsupported, "json_document images need a little-endian target"); // LCOV_EXCL_LINE
-#endif
     if (image == nullptr || size < sizeof(image_header))
     {
         throw_invalid_image("too short");
@@ -738,6 +735,7 @@ inline void load_image(document_data& d, const std::uint8_t* image, std::size_t
     std::vector<std::uint32_t>().swap(d.large_objects); // (only needed while building)
     d.discarded = false;
 }
+#endif
 
 }  // namespace view
 }  // namespace detail

include/nlohmann/detail/view/simd.hpp

@@ -24,25 +24,25 @@
 // with different flags would have different definitions of the same inline
 // functions): the check is compiled for SSSE3 with a function attribute and
 // used where the CPU has SSSE3 (all x86-64 CPUs since about 2011), else the
-// portable check. JSON_VIEW_USE_SSSE3 skips the CPU check (for code compiled
+// portable check. Code compiled for SSSE3 anyway (-mssse3 or more) skips the
-// for SSSE3 anyway); JSON_VIEW_NO_SIMD selects the portable code.
+// CPU check. JSON_NO_SIMD selects the portable code, as in the lexer.
 // NLOHMANN_VIEW_NO_TARGET_ATTRIBUTE (set by the GCC module interface, where GCC
 // ignores the target attribute and then rejects the SSSE3 intrinsics) keeps the
 // check portable without disabling the SSE2 code.
-#if !defined(JSON_VIEW_NO_SIMD) && defined(__aarch64__) && (defined(__GNUC__) || defined(__clang__)) && NLOHMANN_VIEW_LITTLE_ENDIAN
+#if !defined(JSON_NO_SIMD) && defined(__aarch64__) && (defined(__GNUC__) || defined(__clang__)) && NLOHMANN_VIEW_LITTLE_ENDIAN
     #include <arm_neon.h>
     #define NLOHMANN_VIEW_NEON 1
 #else
     #define NLOHMANN_VIEW_NEON 0
 #endif
 // (x86 only: other targets can define __SSE2__ as well, e.g., WebAssembly with -msse2, but have no <cpuid.h>)
-#if !defined(JSON_VIEW_NO_SIMD) && !NLOHMANN_VIEW_NEON && (defined(__x86_64__) || defined(__i386__) || defined(_M_X64) || defined(_M_IX86)) && (defined(__SSE2__) || defined(_M_X64) || (defined(_M_IX86_FP) && _M_IX86_FP >= 2))
+#if !defined(JSON_NO_SIMD) && !NLOHMANN_VIEW_NEON && (defined(__x86_64__) || defined(__i386__) || defined(_M_X64) || defined(_M_IX86)) && (defined(__SSE2__) || defined(_M_X64) || (defined(_M_IX86_FP) && _M_IX86_FP >= 2))
     #include <emmintrin.h>
     #define NLOHMANN_VIEW_SSE2 1
 #else
     #define NLOHMANN_VIEW_SSE2 0
 #endif
-#if NLOHMANN_VIEW_SSE2 && defined(JSON_VIEW_USE_SSSE3)
+#if NLOHMANN_VIEW_SSE2 && defined(__SSSE3__)
     #include <tmmintrin.h>
     #define NLOHMANN_VIEW_SSSE3 1 // NOLINT(cppcoreguidelines-macro-to-enum,modernize-macro-to-enum)
 #else

include/nlohmann/json_view.hpp

@@ -106,6 +106,8 @@ class basic_json_view
     using navigation = detail::view::navigation<is_editable>;
 
   public:
+    /// the basic_json type of the document (it also marks views for is_json_view)
+    using basic_json_type = BasicJsonType;
     using value_t = detail::value_t;
     using string_t = typename BasicJsonType::string_t;
     using number_integer_t = typename BasicJsonType::number_integer_t;
@@ -567,8 +569,10 @@ class basic_json_view
 
     /// the value converted to T, as BasicJsonType::get<T>(): arithmetic types,
     /// strings (string_view_t without a copy), std::nullptr_t, std::vector,
-    /// maps with string keys, and views are converted directly; other types
+    /// maps with string keys, and views are converted directly; types whose
-    /// through materialize().get<T>()
+    /// from_json() accepts views (those of the NLOHMANN_DEFINE_TYPE_* and
+    /// NLOHMANN_JSON_SERIALIZE_ENUM macros, say) read the view; other types
+    /// go through materialize().get<T>()
     template<typename T>
     NLOHMANN_VIEW_ALWAYS_INLINE T get() const
     {
@@ -576,11 +580,12 @@ class basic_json_view
     }
 
     /// as BasicJsonType::get_to(): the types get<T>() converts directly are
-    /// assigned, all others are passed to from_json with v as it is
+    /// assigned, all others are passed to from_json with v as it is (with
+    /// the view if from_json() accepts views, else with materialize())
     template<typename T>
     T& get_to(T& v) const
     {
-        get_to_impl(v, detail::view::is_direct_value<T, BasicJsonType, basic_json_view> {});
+        get_to_impl(v, get_to_kind<T> {});
         return v;
     }
 
@@ -923,6 +928,26 @@ class basic_json_view
         return detail::view::map_value<std::unordered_map<K, V, H, E, A>>(*this);
     }
 
+    /// whether the from_json() of T's serializer reads views (see
+    /// detail::has_view_from_json)
+    template<typename T>
+    using reads_view = detail::has_view_from_json<typename BasicJsonType::template json_serializer<T, void>, basic_json_view, T>;
+
+    /// how get_to() converts: 2 directly, 1 with a from_json() that reads
+    /// views, 0 through materialize()
+    template<typename T>
+    using get_to_kind = std::integral_constant < int, detail::view::is_direct_value<T, BasicJsonType, basic_json_view>::value
+                        ? 2 : static_cast<int>(reads_view<T>::value) >;
+
+    /// types whose from_json() reads views, without materialize()
+    template < typename T, typename std::enable_if < reads_view<T>::value && std::is_default_constructible<T>::value, int >::type = 0 >
+    T get_impl(detail::view::value_tag<T> /*unused*/, detail::priority_tag<1> /*unused*/) const
+    {
+        auto v = T();
+        BasicJsonType::template json_serializer<T, void>::from_json(*this, v);
+        return v;
+    }
+
     /// everything else through the BasicJsonType value (from_json included)
     template<typename T>
     T get_impl(detail::view::value_tag<T> /*unused*/, detail::priority_tag<0> /*unused*/) const
@@ -933,14 +958,20 @@ class basic_json_view
     // --- get_to() dispatch ---
 
     template<typename T>
-    void get_to_impl(T& v, std::true_type /*direct*/) const
+    void get_to_impl(T& v, std::integral_constant<int, 2> /*direct*/) const
     {
         v = get<T>();
     }
 
     /// from_json may keep parts of v (members a JSON object lacks, say)
     template<typename T>
-    void get_to_impl(T& v, std::false_type /*direct*/) const
+    void get_to_impl(T& v, std::integral_constant<int, 1> /*from_json reads views*/) const
+    {
+        BasicJsonType::template json_serializer<T, void>::from_json(*this, v);
+    }
+
+    template<typename T>
+    void get_to_impl(T& v, std::integral_constant<int, 0> /*through materialize()*/) const
     {
         materialize().get_to(v);
     }
@@ -1182,6 +1213,10 @@ class basic_json_document
     /// how load() checks an image (full, bounds, or none)
     using image_check = detail::view::image_check;
 
+#if NLOHMANN_VIEW_LITTLE_ENDIAN
+    // (the image format is little-endian: big-endian targets have no save()
+    // and load(), so that a call fails to compile instead of always throwing)
+
     /// The document as an image that load() reads without parsing: the node
     /// index, the text, and the decoded strings. An edited document is
     /// written in its current state (floats that are not finite become null,
@@ -1223,6 +1258,7 @@ class basic_json_document
         detail::view::load_image(*d.m_data, d.m_data->owned_image.data(), d.m_data->owned_image.size(), check);
         return d;
     }
+#endif
 
     ///////////
     // edits //
@@ -1640,6 +1676,15 @@ class basic_json_document
     std::unique_ptr<document_data, document_data::deleter> m_data{}; // NOLINT(readability-redundant-member-init)
 };
 
+/*!
+@brief whether T is a basic_json_view (of any BasicJsonType and view_mode)
+
+For constraining templates that accept views, e.g. a from_json() written for
+both basic_json values and views.
+*/
+template<typename T>
+struct is_json_view : detail::is_json_view<T> {};
+
 /// a parsed JSON text for json
 using json_document = basic_json_document<json>;
 /// a value of a json_document

single_include/nlohmann/json.hpp

@@ -193,26 +193,14 @@
     #define NLOHMANN_JSON_ABI_TAG_NO_SIMD
 #endif
 
-#ifdef JSON_VIEW_NO_SIMD
-    #define NLOHMANN_JSON_ABI_TAG_VIEW_NO_SIMD _vns
-#else
-    #define NLOHMANN_JSON_ABI_TAG_VIEW_NO_SIMD
-#endif
-
-#ifdef JSON_VIEW_USE_SSSE3
-    #define NLOHMANN_JSON_ABI_TAG_VIEW_USE_SSSE3 _vssse3
-#else
-    #define NLOHMANN_JSON_ABI_TAG_VIEW_USE_SSSE3
-#endif
-
 #ifndef NLOHMANN_JSON_NAMESPACE_NO_VERSION
     #define NLOHMANN_JSON_NAMESPACE_NO_VERSION 0
 #endif
 
 // Construct the namespace ABI tags component
-#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g, h, i, j, k, l, m) json_abi ## a ## b ## c ## d ## e ## f ## g ## h ## i ## j ## k ## l ## m
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g, h, i, j, k) json_abi ## a ## b ## c ## d ## e ## f ## g ## h ## i ## j ## k
-#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f, g, h, i, j, k, l, m) \
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f, g, h, i, j, k) \
-    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g, h, i, j, k, l, m)
+    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g, h, i, j, k)
 
 #define NLOHMANN_JSON_ABI_TAGS                                       \
     NLOHMANN_JSON_ABI_TAGS_CONCAT(                                   \
@@ -226,9 +214,7 @@
             NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS,       \
             NLOHMANN_JSON_ABI_TAG_DISABLE_STREAM_BULK_SCAN,          \
             NLOHMANN_JSON_ABI_TAG_DISABLE_UNLOCKED_FILE_IO,          \
-            NLOHMANN_JSON_ABI_TAG_NO_SIMD,                           \
+            NLOHMANN_JSON_ABI_TAG_NO_SIMD)
-            NLOHMANN_JSON_ABI_TAG_VIEW_NO_SIMD,                      \
-            NLOHMANN_JSON_ABI_TAG_VIEW_USE_SSSE3)
 
 // Construct the namespace version component
 #define NLOHMANN_JSON_NAMESPACE_VERSION_CONCAT_EX(major, minor, patch) \
@@ -286,6 +272,7 @@
 
 #include <algorithm> // min, transform
 #include <array> // array
+#include <cstddef> // nullptr_t
 #include <forward_list> // forward_list
 #include <iterator> // inserter, front_inserter, end
 #include <map> // map
@@ -2677,15 +2664,17 @@ JSON_HEDLEY_DIAGNOSTIC_POP
         });                                                                                     \
         j = ((it != std::end(m)) ? it : std::begin(m))->second;                                 \
     }                                                                                           \
-    template<typename BasicJsonType>                                                            \
+    template<typename BasicJsonType, nlohmann::detail::enable_if_t<nlohmann::detail::is_basic_json_or_view<BasicJsonType>::value, int> = 0> \
     inline void from_json(const BasicJsonType& j, ENUM_TYPE& e)                                 \
     {                                                                                           \
         /* NOLINTNEXTLINE(modernize-type-traits) we use C++11 */                                \
         static_assert(std::is_enum<ENUM_TYPE>::value, #ENUM_TYPE " must be an enum!");          \
+        /* (for a view, the table holds basic_json values, which compare with the view) */      \
+        using nlohmann_json_value_t = nlohmann::detail::json_type_of_t<BasicJsonType>;          \
         /* NOLINTNEXTLINE(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) we don't want to depend on <array> */ \
-        static const std::pair<ENUM_TYPE, BasicJsonType> m[] = __VA_ARGS__;                     \
+        static const std::pair<ENUM_TYPE, nlohmann_json_value_t> m[] = __VA_ARGS__;             \
         auto it = std::find_if(std::begin(m), std::end(m),                                      \
-                               [&j](const std::pair<ENUM_TYPE, BasicJsonType>& ej_pair) -> bool \
+                               [&j](const std::pair<ENUM_TYPE, nlohmann_json_value_t>& ej_pair) -> bool \
         {                                                                                       \
             return ej_pair.second == j;                                                         \
         });                                                                                     \
@@ -2716,20 +2705,22 @@ JSON_HEDLEY_DIAGNOSTIC_POP
         if (it != std::end(m)) j = it->second;                                                  \
         else ::nlohmann::detail::templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(nlohmann::detail::exception_id::value_out_of_range,"enum value out of range for " #ENUM_TYPE, nullptr)); \
     }                                                                                           \
-    template<typename BasicJsonType>                                                            \
+    template<typename BasicJsonType, nlohmann::detail::enable_if_t<nlohmann::detail::is_basic_json_or_view<BasicJsonType>::value, int> = 0> \
     inline void from_json(const BasicJsonType& j, ENUM_TYPE& e)                                 \
     {                                                                                           \
         /* NOLINTNEXTLINE(modernize-type-traits) we use C++11 */                                \
         static_assert(std::is_enum<ENUM_TYPE>::value, #ENUM_TYPE " must be an enum!");          \
+        /* (for a view, the table holds basic_json values, which compare with the view) */      \
+        using nlohmann_json_value_t = nlohmann::detail::json_type_of_t<BasicJsonType>;          \
         /* NOLINTNEXTLINE(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) we don't want to depend on <array> */ \
-        static const std::pair<ENUM_TYPE, BasicJsonType> m[] = __VA_ARGS__;                     \
+        static const std::pair<ENUM_TYPE, nlohmann_json_value_t> m[] = __VA_ARGS__;             \
         auto it = std::find_if(std::begin(m), std::end(m),                                      \
-                               [&j](const std::pair<ENUM_TYPE, BasicJsonType>& ej_pair) -> bool \
+                               [&j](const std::pair<ENUM_TYPE, nlohmann_json_value_t>& ej_pair) -> bool \
         {                                                                                       \
             return ej_pair.second == j;                                                         \
         });                                                                                     \
         if (it != std::end(m)) e = it->first;                                                   \
-        else ::nlohmann::detail::templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(nlohmann::detail::exception_id::value_out_of_range, nlohmann::detail::concat("enum value out of range for " #ENUM_TYPE ": ", j.dump(-1, ' ', false, nlohmann::detail::error_handler_t::replace)), &j)); \
+        else ::nlohmann::detail::templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(nlohmann::detail::exception_id::value_out_of_range, nlohmann::detail::concat("enum value out of range for " #ENUM_TYPE ": ", nlohmann::detail::from_json_dump(j)), nlohmann::detail::from_json_context(j))); \
     }
 
 // Ugly macros to avoid uglier copy-paste when specializing basic_json. They
@@ -2989,6 +2980,8 @@ JSON_HEDLEY_DIAGNOSTIC_POP
 #define NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME(v1, v2) nlohmann_json_t.v2 = !nlohmann_json_j.is_null() ? nlohmann_json_j.value(v1, nlohmann_json_default_obj.v2) : nlohmann_json_default_obj.v2;
 
 #define NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(...) template<typename BasicJsonType, nlohmann::detail::enable_if_t<nlohmann::detail::is_basic_json<BasicJsonType>::value, int> = 0> __VA_ARGS__
+// from_json() also reads from the views of <nlohmann/json_view.hpp>
+#define NLOHMANN_JSON_FROM_TYPE_TEMPLATE(...) template<typename BasicJsonType, nlohmann::detail::enable_if_t<nlohmann::detail::is_basic_json_or_view<BasicJsonType>::value, int> = 0> __VA_ARGS__
 
 // Helpers used to dispatch the NLOHMANN_DEFINE_TYPE_*/NLOHMANN_DEFINE_DERIVED_TYPE_*
 // macros below between a zero-member and a one-or-more-member implementation
@@ -3041,18 +3034,18 @@ JSON_HEDLEY_DIAGNOSTIC_POP
 */
 #define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_MEMBERS(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
 #define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_EMPTY(Type)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); }) \
     /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type is used as a declarator type, not in an expression */ \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType&, Type&) noexcept { })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType&, Type&) noexcept { })
 
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_TYPE_BODY(NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_, __VA_ARGS__)(__VA_ARGS__))
 
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
 
 /*!
 @brief macro
@@ -3062,7 +3055,7 @@ JSON_HEDLEY_DIAGNOSTIC_POP
 */
 #define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_MEMBERS(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
 // identical to NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_EMPTY: with no members there is nothing to default
 #define NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_EMPTY(Type) NLOHMANN_JSON_DEFINE_TYPE_INTRUSIVE_EMPTY(Type)
@@ -3071,7 +3064,7 @@ JSON_HEDLEY_DIAGNOSTIC_POP
 
 #define NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
 
 /*!
 @brief macro
@@ -3098,18 +3091,18 @@ JSON_HEDLEY_DIAGNOSTIC_POP
 */
 #define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_MEMBERS(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
 #define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_EMPTY(Type)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type&) { nlohmann_json_j = BasicJsonType::object(); }) \
     /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type is used as a declarator type, not in an expression */ \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType&, Type&) noexcept { })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType&, Type&) noexcept { })
 
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_TYPE_BODY(NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_, __VA_ARGS__)(__VA_ARGS__))
 
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
 
 /*!
 @brief macro
@@ -3119,7 +3112,7 @@ JSON_HEDLEY_DIAGNOSTIC_POP
 */
 #define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_MEMBERS(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
 // identical to NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_EMPTY: with no members there is nothing to default
 #define NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_EMPTY(Type) NLOHMANN_JSON_DEFINE_TYPE_NON_INTRUSIVE_EMPTY(Type)
@@ -3128,7 +3121,7 @@ JSON_HEDLEY_DIAGNOSTIC_POP
 
 #define NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
 
 /*!
 @brief macro
@@ -3155,18 +3148,18 @@ JSON_HEDLEY_DIAGNOSTIC_POP
 */
 #define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_MEMBERS(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
 #define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_EMPTY(Type, BaseType)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); }) \
     /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type/BaseType are used as declarator types, not in expressions */ \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
 
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DERIVED_TYPE_BODY(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_, __VA_ARGS__)(__VA_ARGS__))
 
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
 
 /*!
 @brief macro
@@ -3176,7 +3169,7 @@ JSON_HEDLEY_DIAGNOSTIC_POP
 */
 #define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_MEMBERS(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
 // identical to NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_EMPTY: with no members there is nothing to default
 #define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_EMPTY(Type, BaseType) NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_EMPTY(Type, BaseType)
@@ -3185,7 +3178,7 @@ JSON_HEDLEY_DIAGNOSTIC_POP
 
 #define NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(friend void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
 
 /*!
 @brief macro
@@ -3213,18 +3206,18 @@ JSON_HEDLEY_DIAGNOSTIC_POP
 */
 #define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_MEMBERS(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM, __VA_ARGS__)) })
 
 #define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_EMPTY(Type, BaseType)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); }) \
     /* NOLINTNEXTLINE(bugprone-macro-parentheses) Type/BaseType are used as declarator types, not in expressions */ \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); })
 
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(...) NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DERIVED_TYPE_BODY(NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_, __VA_ARGS__)(__VA_ARGS__))
 
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_NAME, __VA_ARGS__)) })
 
 /*!
 @brief macro
@@ -3234,7 +3227,7 @@ JSON_HEDLEY_DIAGNOSTIC_POP
 */
 #define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_MEMBERS(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_TO, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT, __VA_ARGS__)) })
 
 // identical to NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_EMPTY: with no members there is nothing to default
 #define NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_EMPTY(Type, BaseType) NLOHMANN_JSON_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_EMPTY(Type, BaseType)
@@ -3243,7 +3236,7 @@ JSON_HEDLEY_DIAGNOSTIC_POP
 
 #define NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES(Type, BaseType, ...)  \
     NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void to_json(BasicJsonType& nlohmann_json_j, const Type& nlohmann_json_t) { nlohmann::to_json(nlohmann_json_j, static_cast<const BaseType &>(nlohmann_json_t)); NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_TO_WITH_NAME, __VA_ARGS__)) }) \
-    NLOHMANN_JSON_BASIC_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { nlohmann::from_json(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
+    NLOHMANN_JSON_FROM_TYPE_TEMPLATE(void from_json(const BasicJsonType& nlohmann_json_j, Type& nlohmann_json_t) { ::nlohmann::detail::from_json_base(nlohmann_json_j, static_cast<BaseType&>(nlohmann_json_t)); const Type nlohmann_json_default_obj{}; NLOHMANN_JSON_EXPAND(NLOHMANN_JSON_DOUBLE_PASTE(NLOHMANN_JSON_FROM_WITH_DEFAULT_WITH_NAME, __VA_ARGS__)) })
 
 /*!
 @brief macro
@@ -4530,6 +4523,47 @@ template<class B> struct negation : std::integral_constant < bool, !B::value > {
 
 #endif
 
+///////////////////////
+// json_view helpers //
+///////////////////////
+
+template<typename T>
+using basic_json_type_t = typename T::basic_json_type;
+
+template<typename T>
+using materialize_function_t = decltype(std::declval<const T&>().materialize());
+
+// a basic_json_view of <nlohmann/json_view.hpp> (detected by its member type
+// basic_json_type, a basic_json, and materialize() returning that type, so that
+// json.hpp needs no declaration of the view)
+template<typename T, typename = void>
+struct is_json_view : std::false_type {};
+
+template<typename T>
+struct is_json_view<T, enable_if_t<is_basic_json<detected_t<basic_json_type_t, T>>::value>>
+    : std::is_same<detected_t<materialize_function_t, T>, basic_json_type_t<T>> {};
+
+// the types from_json() functions of the NLOHMANN_DEFINE_TYPE_* and
+// NLOHMANN_JSON_SERIALIZE_ENUM macros read from
+template<typename T>
+struct is_basic_json_or_view : disjunction<is_basic_json<T>, is_json_view<T>> {};
+
+// the basic_json type of a basic_json value or of a view
+template<typename T, typename = void>
+struct json_type_of
+{
+    using type = T;
+};
+
+template<typename T>
+struct json_type_of<T, enable_if_t<is_json_view<T>::value>>
+{
+    using type = typename T::basic_json_type;
+};
+
+template<typename T>
+using json_type_of_t = typename json_type_of<T>::type;
+
 // Reimplementation of is_constructible and is_default_constructible, due to them being broken for
 // std::pair and std::tuple until LWG 2367 fix (see https://cplusplus.github.io/LWG/lwg-defects.html#2367).
 // This causes compile errors in e.g., Clang 3.5 or GCC 4.9.
@@ -5565,7 +5599,7 @@ enum class exception_id : int
     type_not_serializable = 317, ///< a value cannot be serialized to the requested binary format
     enum_key_duplicate = 318, ///< an enum-keyed map has two keys that serialize to the same string
     document_binary_value = 319, ///< a binary value is stored in a json_document
-    document_image_unsupported = 320, ///< a json_document image cannot be saved or loaded (discarded document, big-endian target)
+    document_image_unsupported = 320, ///< a discarded json_document cannot be saved as an image
     discarded_value_used = 321, ///< a discarded value is used
     // out_of_range
     array_index_out_of_range = 401, ///< an array index is out of range
@@ -6049,6 +6083,59 @@ NLOHMANN_JSON_NAMESPACE_END
 
 // #include <nlohmann/detail/meta/type_traits.hpp>
 
+// #include <nlohmann/detail/output/error_handler.hpp>
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+
+
+// #include <nlohmann/detail/abi_macros.hpp>
+
+
+NLOHMANN_JSON_NAMESPACE_BEGIN
+namespace detail
+{
+
+/// how to treat decoding errors
+///
+/// @ref basic_json::dump uses this to decide what to do with ill-formed
+/// UTF-8 while escaping a string, and the binary writers (@ref
+/// basic_json::to_cbor, @ref basic_json::to_ubjson, @ref
+/// basic_json::to_bjdata, @ref basic_json::to_bson) use it the same way for
+/// string values and object keys. The binary readers (@ref
+/// basic_json::from_cbor, @ref basic_json::from_msgpack, @ref
+/// basic_json::from_ubjson, @ref basic_json::from_bjdata, @ref
+/// basic_json::from_bson) use it to decide whether to check text strings
+/// and object keys for well-formed UTF-8 at all, since none of those
+/// formats requires a decoder to do so.
+enum class error_handler_t
+{
+    strict,  ///< throw a type_error/parse_error exception in case of invalid UTF-8
+    replace, ///< replace invalid UTF-8 sequences with U+FFFD
+    ignore,  ///< ignore invalid UTF-8 sequences
+    keep     ///< keep invalid UTF-8 sequences unchanged
+};
+
+/// the default error handler of the CBOR, UBJSON, BJData, and BSON writers:
+/// error_handler_t::strict if JSON_STRICT_BINARY_UTF8 is enabled, otherwise
+/// error_handler_t::keep (the behavior before version 3.13.0)
+constexpr error_handler_t binary_writer_default_error_handler() noexcept
+{
+#if JSON_STRICT_BINARY_UTF8
+    return error_handler_t::strict;
+#else
+    return error_handler_t::keep;
+#endif
+}
+
+}  // namespace detail
+NLOHMANN_JSON_NAMESPACE_END
+
 // #include <nlohmann/detail/string_concat.hpp>
 
 // #include <nlohmann/detail/value_t.hpp>
@@ -6689,16 +6776,114 @@ inline void from_json(const BasicJsonType& j, std_fs::path& p)
 }
 #endif
 
-struct from_json_fn
+namespace from_json_adl
 {
-    template<typename BasicJsonType, typename T>
+// hides the library's from_json() overloads above (and the from_json object):
-    auto operator()(const BasicJsonType& j, T&& val) const
+// a call from this namespace finds only the from_json() functions of the
+// arguments' own namespaces and classes (ADL); the declaration is never viable
+// and never defined (not "= delete", which GCC before 6 reports as a use)
+struct hidden;
+void from_json(const hidden&);
+
+// a type no from_json() written for JSON values accepts: a from_json() that
+// accepts it is not constrained to them (see has_view_from_json; it lives
+// here, so that ADL finds no other from_json() for it)
+struct probe
+{};
+
+struct fn
+{
+    template<typename SourceType, typename T>
+    auto operator()(const SourceType& j, T&& val) const
     noexcept(noexcept(from_json(j, std::forward<T>(val))))
     -> decltype(from_json(j, std::forward<T>(val)))
     {
         return from_json(j, std::forward<T>(val));
     }
 };
+}  // namespace from_json_adl
+
+// the sources whose from_json() is only looked up by ADL: views (the library's
+// overloads are written for basic_json) and the probe
+template<typename T>
+struct is_adl_only_from_json_source : disjunction<is_json_view<T>, std::is_same<T, from_json_adl::probe>> {};
+
+struct from_json_fn
+{
+    template < typename BasicJsonType, typename T,
+               enable_if_t < !is_adl_only_from_json_source<BasicJsonType>::value, int > = 0 >
+    auto operator()(const BasicJsonType& j, T && val) const
+    noexcept(noexcept(from_json(j, std::forward<T>(val))))
+    -> decltype(from_json(j, std::forward<T>(val)))
+    {
+        return from_json(j, std::forward<T>(val));
+    }
+
+    template < typename SourceType, typename T,
+               enable_if_t < is_adl_only_from_json_source<SourceType>::value, int > = 0 >
+    auto operator()(const SourceType& j, T && val) const
+    noexcept(noexcept(from_json_adl::fn {}(j, std::forward<T>(val))))
+    -> decltype(from_json_adl::fn {}(j, std::forward<T>(val)))
+    {
+        return from_json_adl::fn {}(j, std::forward<T>(val));
+    }
+};
+
+// Whether JSONSerializer::from_json(view, T&) reads T from a view (of
+// <nlohmann/json_view.hpp>) directly: it must accept the view but not the
+// probe. An unconstrained from_json() template (written for basic_json, but
+// accepting anything) is thus not called with a view, nor are the library's
+// own conversions; the view converts such types through materialize().
+template<typename Serializer, typename SourceType, typename T>
+using serializer_from_json_t = decltype(Serializer::from_json(std::declval<const SourceType&>(), std::declval<T&>()));
+
+template<typename Serializer, typename View, typename T>
+struct has_view_from_json
+    : conjunction < is_detected<serializer_from_json_t, Serializer, View, T>,
+      negation<is_detected<serializer_from_json_t, Serializer, from_json_adl::probe, T>>> {};
+
+// the base part of a type of the NLOHMANN_DEFINE_DERIVED_TYPE_* macros: from a
+// view through its get_to(), which reads the base from the view where the
+// base's from_json() accepts views, and from materialize() otherwise
+template<typename BasicJsonType, typename T, enable_if_t<is_basic_json<BasicJsonType>::value, int> = 0>
+void from_json_base(const BasicJsonType& j, T& base)
+{
+    from_json_fn {}(j, base);
+}
+
+template<typename View, typename T, enable_if_t<is_json_view<View>::value, int> = 0>
+void from_json_base(const View& v, T& base)
+{
+    v.get_to(base);
+}
+
+// the context of an exception thrown by a from_json() of the macros: the value
+// itself for basic_json (for JSON_DIAGNOSTICS), none for a view
+template<typename BasicJsonType, enable_if_t<is_basic_json<BasicJsonType>::value, int> = 0>
+const BasicJsonType * from_json_context(const BasicJsonType& j) noexcept
+{
+    return &j;
+}
+
+template<typename View, enable_if_t<is_json_view<View>::value, int> = 0>
+std::nullptr_t from_json_context(const View& /*unused*/) noexcept
+{
+    return nullptr;
+}
+
+// a value as an exception message shows it (invalid UTF-8 replaced; the
+// strings of a view are always valid UTF-8)
+template<typename BasicJsonType, enable_if_t<is_basic_json<BasicJsonType>::value, int> = 0>
+typename BasicJsonType::string_t from_json_dump(const BasicJsonType& j)
+{
+    return j.dump(-1, ' ', false, error_handler_t::replace);
+}
+
+template<typename View, enable_if_t<is_json_view<View>::value, int> = 0>
+typename View::string_t from_json_dump(const View& v)
+{
+    return v.dump();
+}
 
 }  // namespace detail
 
@@ -6793,57 +6978,6 @@ NLOHMANN_JSON_NAMESPACE_END
 // #include <nlohmann/detail/macro_scope.hpp>
 
 // #include <nlohmann/detail/output/error_handler.hpp>
-//     __ _____ _____ _____
-//  __|  |   __|     |   | |  JSON for Modern C++
-// |  |  |__   |  |  | | | |  version 3.12.0
-// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
-//
-// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
-// SPDX-License-Identifier: MIT
-
-
-
-// #include <nlohmann/detail/abi_macros.hpp>
-
-
-NLOHMANN_JSON_NAMESPACE_BEGIN
-namespace detail
-{
-
-/// how to treat decoding errors
-///
-/// @ref basic_json::dump uses this to decide what to do with ill-formed
-/// UTF-8 while escaping a string, and the binary writers (@ref
-/// basic_json::to_cbor, @ref basic_json::to_ubjson, @ref
-/// basic_json::to_bjdata, @ref basic_json::to_bson) use it the same way for
-/// string values and object keys. The binary readers (@ref
-/// basic_json::from_cbor, @ref basic_json::from_msgpack, @ref
-/// basic_json::from_ubjson, @ref basic_json::from_bjdata, @ref
-/// basic_json::from_bson) use it to decide whether to check text strings
-/// and object keys for well-formed UTF-8 at all, since none of those
-/// formats requires a decoder to do so.
-enum class error_handler_t
-{
-    strict,  ///< throw a type_error/parse_error exception in case of invalid UTF-8
-    replace, ///< replace invalid UTF-8 sequences with U+FFFD
-    ignore,  ///< ignore invalid UTF-8 sequences
-    keep     ///< keep invalid UTF-8 sequences unchanged
-};
-
-/// the default error handler of the CBOR, UBJSON, BJData, and BSON writers:
-/// error_handler_t::strict if JSON_STRICT_BINARY_UTF8 is enabled, otherwise
-/// error_handler_t::keep (the behavior before version 3.13.0)
-constexpr error_handler_t binary_writer_default_error_handler() noexcept
-{
-#if JSON_STRICT_BINARY_UTF8
-    return error_handler_t::strict;
-#else
-    return error_handler_t::keep;
-#endif
-}
-
-}  // namespace detail
-NLOHMANN_JSON_NAMESPACE_END
 
 
 NLOHMANN_JSON_NAMESPACE_BEGIN

single_include/nlohmann/json_fwd.hpp

@@ -145,26 +145,14 @@
     #define NLOHMANN_JSON_ABI_TAG_NO_SIMD
 #endif
 
-#ifdef JSON_VIEW_NO_SIMD
-    #define NLOHMANN_JSON_ABI_TAG_VIEW_NO_SIMD _vns
-#else
-    #define NLOHMANN_JSON_ABI_TAG_VIEW_NO_SIMD
-#endif
-
-#ifdef JSON_VIEW_USE_SSSE3
-    #define NLOHMANN_JSON_ABI_TAG_VIEW_USE_SSSE3 _vssse3
-#else
-    #define NLOHMANN_JSON_ABI_TAG_VIEW_USE_SSSE3
-#endif
-
 #ifndef NLOHMANN_JSON_NAMESPACE_NO_VERSION
     #define NLOHMANN_JSON_NAMESPACE_NO_VERSION 0
 #endif
 
 // Construct the namespace ABI tags component
-#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g, h, i, j, k, l, m) json_abi ## a ## b ## c ## d ## e ## f ## g ## h ## i ## j ## k ## l ## m
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g, h, i, j, k) json_abi ## a ## b ## c ## d ## e ## f ## g ## h ## i ## j ## k
-#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f, g, h, i, j, k, l, m) \
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c, d, e, f, g, h, i, j, k) \
-    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g, h, i, j, k, l, m)
+    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c, d, e, f, g, h, i, j, k)
 
 #define NLOHMANN_JSON_ABI_TAGS                                       \
     NLOHMANN_JSON_ABI_TAGS_CONCAT(                                   \
@@ -178,9 +166,7 @@
             NLOHMANN_JSON_ABI_TAG_OBJECTS_FOR_ENUM_KEYED_MAPS,       \
             NLOHMANN_JSON_ABI_TAG_DISABLE_STREAM_BULK_SCAN,          \
             NLOHMANN_JSON_ABI_TAG_DISABLE_UNLOCKED_FILE_IO,          \
-            NLOHMANN_JSON_ABI_TAG_NO_SIMD,                           \
+            NLOHMANN_JSON_ABI_TAG_NO_SIMD)
-            NLOHMANN_JSON_ABI_TAG_VIEW_NO_SIMD,                      \
-            NLOHMANN_JSON_ABI_TAG_VIEW_USE_SSSE3)
 
 // Construct the namespace version component
 #define NLOHMANN_JSON_NAMESPACE_VERSION_CONCAT_EX(major, minor, patch) \

single_include/nlohmann/json_view.hpp

@@ -678,25 +678,25 @@ NLOHMANN_JSON_NAMESPACE_END
 // with different flags would have different definitions of the same inline
 // functions): the check is compiled for SSSE3 with a function attribute and
 // used where the CPU has SSSE3 (all x86-64 CPUs since about 2011), else the
-// portable check. JSON_VIEW_USE_SSSE3 skips the CPU check (for code compiled
+// portable check. Code compiled for SSSE3 anyway (-mssse3 or more) skips the
-// for SSSE3 anyway); JSON_VIEW_NO_SIMD selects the portable code.
+// CPU check. JSON_NO_SIMD selects the portable code, as in the lexer.
 // NLOHMANN_VIEW_NO_TARGET_ATTRIBUTE (set by the GCC module interface, where GCC
 // ignores the target attribute and then rejects the SSSE3 intrinsics) keeps the
 // check portable without disabling the SSE2 code.
-#if !defined(JSON_VIEW_NO_SIMD) && defined(__aarch64__) && (defined(__GNUC__) || defined(__clang__)) && NLOHMANN_VIEW_LITTLE_ENDIAN
+#if !defined(JSON_NO_SIMD) && defined(__aarch64__) && (defined(__GNUC__) || defined(__clang__)) && NLOHMANN_VIEW_LITTLE_ENDIAN
     #include <arm_neon.h>
     #define NLOHMANN_VIEW_NEON 1
 #else
     #define NLOHMANN_VIEW_NEON 0
 #endif
 // (x86 only: other targets can define __SSE2__ as well, e.g., WebAssembly with -msse2, but have no <cpuid.h>)
-#if !defined(JSON_VIEW_NO_SIMD) && !NLOHMANN_VIEW_NEON && (defined(__x86_64__) || defined(__i386__) || defined(_M_X64) || defined(_M_IX86)) && (defined(__SSE2__) || defined(_M_X64) || (defined(_M_IX86_FP) && _M_IX86_FP >= 2))
+#if !defined(JSON_NO_SIMD) && !NLOHMANN_VIEW_NEON && (defined(__x86_64__) || defined(__i386__) || defined(_M_X64) || defined(_M_IX86)) && (defined(__SSE2__) || defined(_M_X64) || (defined(_M_IX86_FP) && _M_IX86_FP >= 2))
     #include <emmintrin.h>
     #define NLOHMANN_VIEW_SSE2 1
 #else
     #define NLOHMANN_VIEW_SSE2 0
 #endif
-#if NLOHMANN_VIEW_SSE2 && defined(JSON_VIEW_USE_SSSE3)
+#if NLOHMANN_VIEW_SSE2 && defined(__SSSE3__)
     #include <tmmintrin.h>
     #define NLOHMANN_VIEW_SSSE3 1 // NOLINT(cppcoreguidelines-macro-to-enum,modernize-macro-to-enum)
 #else
@@ -5007,12 +5007,10 @@ inline void compact_nodes(const document_data& d, std::size_t arena_size, std::v
     }
 }
 
+#if NLOHMANN_VIEW_LITTLE_ENDIAN // (the image format is little-endian: no save() elsewhere)
 /// the document as an image
 inline std::vector<std::uint8_t> save_image(const document_data& d)
 {
-#if !NLOHMANN_VIEW_LITTLE_ENDIAN
-    throw_type_error(exception_id::document_image_unsupported, "json_document images need a little-endian target"); // LCOV_EXCL_LINE
-#endif
     const std::size_t arena_size = d.arena_size;
     std::vector<node> compacted;
     std::string text_tail;
@@ -5068,6 +5066,7 @@ inline std::vector<std::uint8_t> save_image(const document_data& d)
     *o = 0;
     return image;
 }
+#endif
 
 /// the parts of a number token that the checks need
 struct number_token
@@ -5488,13 +5487,11 @@ inline bool check_image(const node* nodes, std::size_t count, const unsigned cha
     throw_parse_error(exception_id::invalid_document_image, concat("invalid json_document image: ", what));
 }
 
+#if NLOHMANN_VIEW_LITTLE_ENDIAN // (the image format is little-endian: no load() elsewhere)
 /// Read an image into d. The text and the decoded strings stay in the image;
 /// the nodes are copied (so that they are aligned, and edits can change them).
 inline void load_image(document_data& d, const std::uint8_t* image, std::size_t size, image_check check)
 {
-#if !NLOHMANN_VIEW_LITTLE_ENDIAN
-    throw_type_error(exception_id::document_image_unsupported, "json_document images need a little-endian target"); // LCOV_EXCL_LINE
-#endif
     if (image == nullptr || size < sizeof(image_header))
     {
         throw_invalid_image("too short");
@@ -5563,6 +5560,7 @@ inline void load_image(document_data& d, const std::uint8_t* image, std::size_t
     std::vector<std::uint32_t>().swap(d.large_objects); // (only needed while building)
     d.discarded = false;
 }
+#endif
 
 }  // namespace view
 }  // namespace detail
@@ -7835,6 +7833,8 @@ class basic_json_view
     using navigation = detail::view::navigation<is_editable>;
 
   public:
+    /// the basic_json type of the document (it also marks views for is_json_view)
+    using basic_json_type = BasicJsonType;
     using value_t = detail::value_t;
     using string_t = typename BasicJsonType::string_t;
     using number_integer_t = typename BasicJsonType::number_integer_t;
@@ -8296,8 +8296,10 @@ class basic_json_view
 
     /// the value converted to T, as BasicJsonType::get<T>(): arithmetic types,
     /// strings (string_view_t without a copy), std::nullptr_t, std::vector,
-    /// maps with string keys, and views are converted directly; other types
+    /// maps with string keys, and views are converted directly; types whose
-    /// through materialize().get<T>()
+    /// from_json() accepts views (those of the NLOHMANN_DEFINE_TYPE_* and
+    /// NLOHMANN_JSON_SERIALIZE_ENUM macros, say) read the view; other types
+    /// go through materialize().get<T>()
     template<typename T>
     NLOHMANN_VIEW_ALWAYS_INLINE T get() const
     {
@@ -8305,11 +8307,12 @@ class basic_json_view
     }
 
     /// as BasicJsonType::get_to(): the types get<T>() converts directly are
-    /// assigned, all others are passed to from_json with v as it is
+    /// assigned, all others are passed to from_json with v as it is (with
+    /// the view if from_json() accepts views, else with materialize())
     template<typename T>
     T& get_to(T& v) const
     {
-        get_to_impl(v, detail::view::is_direct_value<T, BasicJsonType, basic_json_view> {});
+        get_to_impl(v, get_to_kind<T> {});
         return v;
     }
 
@@ -8652,6 +8655,26 @@ class basic_json_view
         return detail::view::map_value<std::unordered_map<K, V, H, E, A>>(*this);
     }
 
+    /// whether the from_json() of T's serializer reads views (see
+    /// detail::has_view_from_json)
+    template<typename T>
+    using reads_view = detail::has_view_from_json<typename BasicJsonType::template json_serializer<T, void>, basic_json_view, T>;
+
+    /// how get_to() converts: 2 directly, 1 with a from_json() that reads
+    /// views, 0 through materialize()
+    template<typename T>
+    using get_to_kind = std::integral_constant < int, detail::view::is_direct_value<T, BasicJsonType, basic_json_view>::value
+                        ? 2 : static_cast<int>(reads_view<T>::value) >;
+
+    /// types whose from_json() reads views, without materialize()
+    template < typename T, typename std::enable_if < reads_view<T>::value && std::is_default_constructible<T>::value, int >::type = 0 >
+    T get_impl(detail::view::value_tag<T> /*unused*/, detail::priority_tag<1> /*unused*/) const
+    {
+        auto v = T();
+        BasicJsonType::template json_serializer<T, void>::from_json(*this, v);
+        return v;
+    }
+
     /// everything else through the BasicJsonType value (from_json included)
     template<typename T>
     T get_impl(detail::view::value_tag<T> /*unused*/, detail::priority_tag<0> /*unused*/) const
@@ -8662,14 +8685,20 @@ class basic_json_view
     // --- get_to() dispatch ---
 
     template<typename T>
-    void get_to_impl(T& v, std::true_type /*direct*/) const
+    void get_to_impl(T& v, std::integral_constant<int, 2> /*direct*/) const
     {
         v = get<T>();
     }
 
     /// from_json may keep parts of v (members a JSON object lacks, say)
     template<typename T>
-    void get_to_impl(T& v, std::false_type /*direct*/) const
+    void get_to_impl(T& v, std::integral_constant<int, 1> /*from_json reads views*/) const
+    {
+        BasicJsonType::template json_serializer<T, void>::from_json(*this, v);
+    }
+
+    template<typename T>
+    void get_to_impl(T& v, std::integral_constant<int, 0> /*through materialize()*/) const
     {
         materialize().get_to(v);
     }
@@ -8911,6 +8940,10 @@ class basic_json_document
     /// how load() checks an image (full, bounds, or none)
     using image_check = detail::view::image_check;
 
+#if NLOHMANN_VIEW_LITTLE_ENDIAN
+    // (the image format is little-endian: big-endian targets have no save()
+    // and load(), so that a call fails to compile instead of always throwing)
+
     /// The document as an image that load() reads without parsing: the node
     /// index, the text, and the decoded strings. An edited document is
     /// written in its current state (floats that are not finite become null,
@@ -8952,6 +8985,7 @@ class basic_json_document
         detail::view::load_image(*d.m_data, d.m_data->owned_image.data(), d.m_data->owned_image.size(), check);
         return d;
     }
+#endif
 
     ///////////
     // edits //
@@ -9369,6 +9403,15 @@ class basic_json_document
     std::unique_ptr<document_data, document_data::deleter> m_data{}; // NOLINT(readability-redundant-member-init)
 };
 
+/*!
+@brief whether T is a basic_json_view (of any BasicJsonType and view_mode)
+
+For constraining templates that accept views, e.g. a from_json() written for
+both basic_json values and views.
+*/
+template<typename T>
+struct is_json_view : detail::is_json_view<T> {};
+
 /// a parsed JSON text for json
 using json_document = basic_json_document<json>;
 /// a value of a json_document

tests/CMakeLists.txt

@@ -420,9 +420,9 @@ json_test_add_test_for(src/unit-file_input.cpp
 )
 
 # the json_view parser again with the portable string scanning instead of
-# NEON/SSE2, and on x86-64 with the SSSE3 UTF-8 check (JSON_VIEW_USE_SSSE3)
+# NEON/SSE2 (JSON_NO_SIMD), and on x86-64 compiled for SSSE3 (no CPU check)
 json_test_set_test_options(test-json_view_builder_portable
-    COMPILE_DEFINITIONS JSON_VIEW_NO_SIMD
+    COMPILE_DEFINITIONS JSON_NO_SIMD
 )
 json_test_add_test_for(src/unit-json_view_builder.cpp
     NAME test-json_view_builder_portable
@@ -430,7 +430,6 @@ json_test_add_test_for(src/unit-json_view_builder.cpp
 )
 if(CMAKE_SYSTEM_PROCESSOR MATCHES "^(x86_64|AMD64|amd64)$" AND NOT MSVC)
     json_test_set_test_options(test-json_view_builder_ssse3
-        COMPILE_DEFINITIONS JSON_VIEW_USE_SSSE3
         COMPILE_OPTIONS -mssse3
     )
     json_test_add_test_for(src/unit-json_view_builder.cpp

tests/abi/config/CMakeLists.txt

@@ -24,9 +24,7 @@ foreach(test default noversion)
         JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON=1
         JSON_DISABLE_STREAM_BULK_SCAN=1
         JSON_DISABLE_UNLOCKED_FILE_IO=1
-        JSON_NO_SIMD
+        JSON_NO_SIMD)
-        JSON_VIEW_NO_SIMD
-        JSON_VIEW_USE_SSSE3)
     target_link_libraries(abi_config_${test}_all_tags PRIVATE abi_compat_main)
     add_test(
         NAME test-abi_config_${test}_all_tags

tests/abi/config/default.cpp

@@ -64,14 +64,6 @@ TEST_CASE("default namespace")
         expected += "_ns";
 #endif
 
-#ifdef JSON_VIEW_NO_SIMD
-        expected += "_vns";
-#endif
-
-#ifdef JSON_VIEW_USE_SSSE3
-        expected += "_vssse3";
-#endif
-
         expected += "_v" STRINGIZE(NLOHMANN_JSON_VERSION_MAJOR);
         expected += "_" STRINGIZE(NLOHMANN_JSON_VERSION_MINOR);
         expected += "_" STRINGIZE(NLOHMANN_JSON_VERSION_PATCH) "::basic_json";

tests/abi/config/noversion.cpp

@@ -65,14 +65,6 @@ TEST_CASE("default namespace without version component")
         expected += "_ns";
 #endif
 
-#ifdef JSON_VIEW_NO_SIMD
-        expected += "_vns";
-#endif
-
-#ifdef JSON_VIEW_USE_SSSE3
-        expected += "_vssse3";
-#endif
-
         expected += "::basic_json";
 
         // fallback for Clang

tests/benchmarks/json_view/README.md

@@ -59,6 +59,12 @@ An editable `json_document` edits in place; yyjson copies its immutable document
 (`yyjson_doc_mut_copy`); Boost.JSON and `json::parse` build mutable DOMs; simdjson cannot edit a document. All
 outputs are checked to describe the same value.
 
+`bench_decode.cpp` measures decoding into structs whose `from_json()` comes from the `NLOHMANN_DEFINE_TYPE_*` macros
+(twitter statuses, citm_catalog performances, and 20,000 synthetic records): `get<T>()` on a view, which reads the
+view directly, against `materialize().get<T>()`, `json::parse` plus `get<T>()`, and `get<T>()` on an already parsed
+`json` value. Only nlohmann/json takes part, as the other libraries have no comparable mapping; all engines are
+checked to decode the same values.
+
 Before anything is timed, all engines must accept each document and agree on the traversal: the number of values, the
 bytes of all strings and keys, and the sum of all numbers. All engines run interleaved in every round, and the best
 round is reported, as time and as a factor of the `json_view` time (below 1 means faster than `json_view`). Each timed

tests/benchmarks/json_view/bench_decode.cpp

@@ -0,0 +1,312 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+// Decoding into structs: the same types, with from_json() generated by the
+// NLOHMANN_DEFINE_TYPE_* macros, read three ways. Only nlohmann/json takes
+// part; the other libraries have no comparable mapping.
+//
+//   view           json_document::parse, then get<T>() on the view (from_json reads the view)
+//   materialize    json_document::parse, then materialize().get<T>() (a json value first)
+//   json::parse    json::parse, then get<T>()
+//   json::get      get<T>() on an already parsed json value (the decoding alone)
+//
+// Documents: twitter (the statuses with their users and hashtags), citm_catalog
+// (the performances with their seat categories), and a synthetic document of
+// 20,000 nested records.
+//
+// Build: see README.md (same flags as bench_view.cpp).
+#include <nlohmann/json_view.hpp>
+
+#include <algorithm>
+#include <chrono>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <fstream>
+#include <functional>
+#include <sstream>
+#include <string>
+#include <utility>
+#include <vector>
+
+using nlohmann::json;
+using nlohmann::json_document;
+
+static volatile std::size_t g_sink;
+
+namespace twitter
+{
+struct hashtag
+{
+    std::string text;
+    std::vector<int> indices;
+};
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(hashtag, text, indices)
+
+struct entities
+{
+    std::vector<hashtag> hashtags;
+};
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(entities, hashtags)
+
+struct user
+{
+    std::uint64_t id = 0;
+    std::string screen_name;
+    std::string description;
+    std::int64_t followers_count = 0;
+};
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(user, id, screen_name, description, followers_count)
+
+struct status
+{
+    std::uint64_t id = 0;
+    std::string text;
+    user user;
+    entities entities;
+    std::int64_t retweet_count = 0;
+    std::int64_t favorite_count = 0;
+};
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(status, id, text, user, entities, retweet_count, favorite_count)
+
+struct document
+{
+    std::vector<status> statuses;
+};
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(document, statuses)
+
+std::size_t digest(const document& d)
+{
+    std::size_t n = 0;
+    for (const auto& s : d.statuses)
+    {
+        n += s.text.size() + s.user.screen_name.size() + s.entities.hashtags.size() + static_cast<std::size_t>(s.retweet_count);
+    }
+    return n;
+}
+}  // namespace twitter
+
+namespace citm
+{
+struct area
+{
+    std::int64_t areaId = 0;
+    std::vector<std::int64_t> blockIds;
+};
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(area, areaId, blockIds)
+
+struct seat_category
+{
+    std::vector<area> areas;
+    std::int64_t seatCategoryId = 0;
+};
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(seat_category, areas, seatCategoryId)
+
+struct performance
+{
+    std::int64_t id = 0;
+    std::int64_t eventId = 0;
+    std::vector<seat_category> seatCategories;
+    std::int64_t start = 0;
+    std::string venueCode;
+};
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(performance, id, eventId, seatCategories, start, venueCode)
+
+struct document
+{
+    std::vector<performance> performances;
+};
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(document, performances)
+
+std::size_t digest(const document& d)
+{
+    std::size_t n = 0;
+    for (const auto& p : d.performances)
+    {
+        n += p.seatCategories.size() + p.venueCode.size() + static_cast<std::size_t>(p.start % 1000);
+        for (const auto& c : p.seatCategories)
+        {
+            n += c.areas.size();
+        }
+    }
+    return n;
+}
+}  // namespace citm
+
+namespace synthetic
+{
+struct position
+{
+    double x = 0;
+    double y = 0;
+};
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(position, x, y)
+
+struct child
+{
+    std::int64_t id = 0;
+    std::string label;
+    bool active = false;
+};
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(child, id, label, active)
+
+struct record
+{
+    std::int64_t id = 0;
+    std::string name;
+    std::vector<std::string> tags;
+    position pos;
+    std::vector<child> children;
+};
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(record, id, name, tags, pos, children)
+
+struct document
+{
+    std::vector<record> records;
+};
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(document, records)
+
+std::string make_text(std::size_t n)
+{
+    std::string s = "{\"records\":[";
+    for (std::size_t i = 0; i < n; ++i)
+    {
+        const std::string id = std::to_string(i);
+        s += (i == 0 ? "" : ",");
+        s += "{\"id\":" + id + ",\"name\":\"record number " + id + "\",\"tags\":[\"alpha\",\"beta\",\"gamma\"],";
+        s += "\"pos\":{\"x\":" + id + ".25,\"y\":-" + id + ".5},\"children\":[";
+        for (std::size_t k = 0; k < 3; ++k)
+        {
+            s += (k == 0 ? "" : ",");
+            s += "{\"id\":" + std::to_string(i * 3 + k) + ",\"label\":\"child " + std::to_string(k) + "\",\"active\":" + (k % 2 == 0 ? "true" : "false") + "}";
+        }
+        s += "]}";
+    }
+    s += "]}";
+    return s;
+}
+
+std::size_t digest(const document& d)
+{
+    std::size_t n = 0;
+    for (const auto& r : d.records)
+    {
+        n += r.name.size() + r.tags.size() + r.children.size() + static_cast<std::size_t>(r.pos.x);
+    }
+    return n;
+}
+}  // namespace synthetic
+
+namespace
+{
+std::string read_file(const std::string& p)
+{
+    std::ifstream f(p, std::ios::binary);
+    if (!f)
+    {
+        std::fprintf(stderr, "cannot open %s\n", p.c_str());
+        std::exit(1);
+    }
+    std::stringstream ss;
+    ss << f.rdbuf();
+    return ss.str();
+}
+
+double time_ns(const std::function<void()>& f)
+{
+    const auto t0 = std::chrono::steady_clock::now();
+    f();
+    const auto t1 = std::chrono::steady_clock::now();
+    return static_cast<double>(std::chrono::duration_cast<std::chrono::nanoseconds>(t1 - t0).count());
+}
+
+struct engine
+{
+    std::string name;
+    std::function<std::size_t()> run;
+};
+
+template<typename Document>
+std::vector<engine> engines(const std::string& text, const json& parsed)
+{
+    return
+    {
+        {"view", [&text] { const json_document d = json_document::parse(text); return digest(d.root().get<Document>()); }},
+        {"materialize", [&text] { const json_document d = json_document::parse(text); return digest(d.root().materialize().get<Document>()); }},
+        {"json::parse", [&text] { return digest(json::parse(text).get<Document>()); }},
+        {"json::get", [&parsed] { return digest(parsed.get<Document>()); }},
+    };
+}
+}  // namespace
+
+int main(int argc, char** argv)
+{
+    if (argc < 2)
+    {
+        std::fprintf(stderr, "usage: %s <json_test_data directory> [rounds]\n", argv[0]);
+        return 1;
+    }
+    const std::string dir = argv[1];
+    const int rounds = argc > 2 ? std::max(1, std::atoi(argv[2])) : 30;
+
+    struct document_case
+    {
+        std::string name;
+        std::string text;
+        json parsed;
+        std::vector<engine> engines;
+    };
+    std::vector<document_case> cases;
+    cases.push_back({"twitter", read_file(dir + "/nativejson-benchmark/twitter.json"), json(), {}});
+    cases.push_back({"citm_catalog", read_file(dir + "/nativejson-benchmark/citm_catalog.json"), json(), {}});
+    cases.push_back({"synthetic", synthetic::make_text(20000), json(), {}});
+    for (auto& c : cases)
+    {
+        c.parsed = json::parse(c.text);
+    }
+    cases[0].engines = engines<twitter::document>(cases[0].text, cases[0].parsed);
+    cases[1].engines = engines<citm::document>(cases[1].text, cases[1].parsed);
+    cases[2].engines = engines<synthetic::document>(cases[2].text, cases[2].parsed);
+
+    std::FILE* csv = std::fopen("bench_decode.csv", "w");
+    if (csv == nullptr)
+    {
+        std::perror("bench_decode.csv");
+        return 1;
+    }
+    std::fprintf(csv, "doc,bytes,engine,ns\n");
+    for (const auto& c : cases)
+    {
+        // all engines must decode the same values
+        const std::size_t expected = c.engines[0].run();
+        bool ok = true;
+        for (const auto& e : c.engines)
+        {
+            ok = ok && e.run() == expected;
+        }
+        std::vector<double> best(c.engines.size(), 1e300);
+        for (int r = 0; r < rounds; ++r)
+        {
+            for (std::size_t k = 0; k < c.engines.size(); ++k)
+            {
+                g_sink = c.engines[k].run(); // untimed: see bench_view.cpp
+                best[k] = std::min(best[k], time_ns([&] { g_sink = c.engines[k].run(); }));
+            }
+        }
+        std::printf("%-13s %-7s %s", c.name.c_str(), "decode", ok ? "" : "[MISMATCH] ");
+        for (std::size_t k = 0; k < c.engines.size(); ++k)
+        {
+            const double us = best[k] / 1000.0;
+            std::printf("  %s %.*fus (%.2fx)", c.engines[k].name.c_str(), us < 10 ? 3 : (us < 1000 ? 1 : 0), us, best[k] / best[0]);
+            std::fprintf(csv, "%s,%zu,%s,%.1f\n", c.name.c_str(), c.text.size(), c.engines[k].name.c_str(), best[k]);
+        }
+        std::printf("\n");
+    }
+    std::fclose(csv);
+    return 0;
+}

tests/benchmarks/json_view/compare.py

@@ -9,7 +9,7 @@
 
 """Compare json_view with yyjson, simdjson, Boost.JSON, and json::parse.
 
-Builds bench_view.cpp, bench_corpus.cpp, and bench_edit.cpp against the include/ directory of
+Builds bench_view.cpp, bench_corpus.cpp, bench_edit.cpp, and bench_decode.cpp against the include/ directory of
 this checkout, runs them, and writes the results with everything needed to
 reproduce them (date, commit, CPU, OS, compiler, library versions, flags) to
 results/<date>-<host>.md and .csv next to this script.
@@ -283,7 +283,7 @@ def main():
             objects.append(obj)
 
     binaries = {}
-    for bench in ['bench_view', 'bench_corpus', 'bench_edit']:
+    for bench in ['bench_view', 'bench_corpus', 'bench_edit', 'bench_decode']:
         exe = os.path.join(args.build_dir, bench)
         run(cxx + flags + include + [os.path.join(HERE, bench + '.cpp')] + objects + link + ['-o', exe])
         binaries[bench] = exe
@@ -297,6 +297,8 @@ def main():
                                   capture_output=True, text=True).stdout
     outputs['bench_edit'] = run([binaries['bench_edit'], args.data, str(max(1, args.rounds // 2))], cwd=args.build_dir,
                                 capture_output=True, text=True).stdout
+    outputs['bench_decode'] = run([binaries['bench_decode'], args.data, str(max(1, args.rounds // 2))], cwd=args.build_dir,
+                                  capture_output=True, text=True).stdout
     for name, text in outputs.items():
         print(text)
 
@@ -330,7 +332,7 @@ def main():
             f.write(f'\n## {name}\n\n```\n{text.rstrip()}\n```\n')
     with open(stem + '.csv', 'w', encoding='utf-8') as out:
         out.write(''.join(f'# {key}: {value}\n' for key, value in meta))
-        for name in ['bench_view', 'bench_corpus', 'bench_edit']:
+        for name in ['bench_view', 'bench_corpus', 'bench_edit', 'bench_decode']:
             path = os.path.join(args.build_dir, name + '.csv')
             if os.path.isfile(path):
                 with open(path, encoding='utf-8') as f:

tests/src/unit-json_view_from_json.cpp

@@ -0,0 +1,357 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json_view.hpp>
+using nlohmann::json;
+using nlohmann::json_document;
+using nlohmann::json_view;
+using nlohmann::json_editable_document;
+using nlohmann::ordered_json_document;
+
+#include "json_view_test_helpers.hpp"
+#if !defined(JSON_NOEXCEPTION)
+    using json_view_test::exception_of_call;
+#endif
+
+#include <array>
+#include <cstddef>
+#include <cstdint>
+#include <deque>
+#include <forward_list>
+#include <list>
+#include <map>
+#include <set>
+#include <string>
+#include <tuple>
+#include <type_traits>
+#include <unordered_map>
+#include <unordered_set>
+#include <utility>
+#include <valarray>
+#include <vector>
+
+#ifdef JSON_HAS_CPP_17
+    #include <optional>
+#endif
+
+// The from_json() functions of the NLOHMANN_DEFINE_TYPE_* and
+// NLOHMANN_JSON_SERIALIZE_ENUM macros read views directly; other from_json()
+// functions get the value of materialize().
+
+namespace view_from_json
+{
+struct point
+{
+    int x = 0;
+    int y = 0;
+    NLOHMANN_DEFINE_TYPE_INTRUSIVE(point, x, y)
+};
+
+struct shape
+{
+    std::string name;
+    std::vector<point> points;
+    point center;
+    std::map<std::string, point> named;
+    NLOHMANN_DEFINE_TYPE_INTRUSIVE(shape, name, points, center, named)
+};
+
+struct with_defaults
+{
+    int a = 1;
+    std::string b = "default";
+    std::vector<int> c = {1, 2};
+};
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(with_defaults, a, b, c)
+
+struct with_names
+{
+    int value = 0;
+    std::string text;
+};
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES(with_names, "Value", value, "Text", text)
+
+struct empty
+{
+    NLOHMANN_DEFINE_TYPE_INTRUSIVE(empty)
+};
+
+enum class color
+{
+    red,
+    green,
+    blue
+};
+NLOHMANN_JSON_SERIALIZE_ENUM(color,
+{
+    {color::red, "red"},
+    {color::green, "green"},
+    {color::blue, nullptr},
+})
+
+enum class strict_color
+{
+    red,
+    green
+};
+NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(strict_color,
+{
+    {strict_color::red, "red"},
+    {strict_color::green, 1},
+})
+
+struct base
+{
+    int id = 0;
+    NLOHMANN_DEFINE_TYPE_INTRUSIVE(base, id)
+};
+
+struct derived : base
+{
+    color c = color::red;
+    NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE(derived, base, c)
+};
+
+struct derived_with_defaults : base
+{
+    std::string label = "none";
+    NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT(derived_with_defaults, base, label)
+};
+
+// a base whose from_json() is written for json only: the derived type reads
+// its own members from the view and the base part from materialize()
+struct legacy_base
+{
+    int id = 0;
+};
+// NOLINTNEXTLINE(misc-use-internal-linkage): found by ADL, like the from_json() functions of users
+inline void from_json(const json& j, legacy_base& b)
+{
+    b.id = j.at("id").get<int>();
+}
+
+struct derived_from_legacy : legacy_base
+{
+    int extra = 0;
+};
+NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE(derived_from_legacy, legacy_base, extra)
+
+// from_json() for json only: converted through materialize()
+struct legacy
+{
+    int v = 0;
+};
+// NOLINTNEXTLINE(misc-use-internal-linkage): found by ADL, like the from_json() functions of users
+inline void from_json(const json& j, legacy& l)
+{
+    l.v = j.at("v").get<int>();
+}
+
+// an unconstrained from_json() template, as in the documentation of
+// arbitrary type conversions: converted through materialize()
+struct unconstrained
+{
+    int v = 0;
+};
+template<typename BasicJsonType>
+// NOLINTNEXTLINE(misc-use-internal-linkage): found by ADL, like the from_json() functions of users
+void from_json(const BasicJsonType& j, unconstrained& u)
+{
+    u.v = j.at("v").template get<int>();
+}
+
+// a from_json() constrained by the user to views and json: reads the view
+struct constrained
+{
+    int v = 0;
+};
+template < typename J, typename std::enable_if < nlohmann::is_json_view<J>::value || std::is_same<J, json>::value, int >::type = 0 >
+// NOLINTNEXTLINE(misc-use-internal-linkage): found by ADL, like the from_json() functions of users
+void from_json(const J& j, constrained& c)
+{
+    c.v = j.at("v").template get<int>();
+}
+}  // namespace view_from_json
+
+namespace
+{
+template<typename T, typename View = json_view>
+struct reads_view : nlohmann::detail::has_view_from_json<nlohmann::adl_serializer<T, void>, View, T> {};
+}  // namespace
+
+TEST_CASE("json_view from_json")
+{
+    using namespace view_from_json; // NOLINT(google-build-using-namespace)
+
+    SECTION("which from_json() functions read views")
+    {
+        static_assert(reads_view<point>::value, "macro types read views");
+        static_assert(reads_view<shape>::value, "macro types read views");
+        static_assert(reads_view<with_defaults>::value, "macro types read views");
+        static_assert(reads_view<with_names>::value, "macro types read views");
+        static_assert(reads_view<empty>::value, "macro types read views");
+        static_assert(reads_view<derived>::value, "macro types read views");
+        static_assert(reads_view<derived_from_legacy>::value, "macro types read views");
+        static_assert(reads_view<color>::value, "enum macro types read views");
+        static_assert(reads_view<strict_color>::value, "enum macro types read views");
+        static_assert(reads_view<constrained>::value, "constrained from_json() reads views");
+        static_assert(reads_view<point, nlohmann::json_editable_view>::value, "editable views as well");
+        static_assert(reads_view<point, nlohmann::ordered_json_view>::value, "views of ordered_json as well");
+        static_assert(!reads_view<legacy>::value, "from_json() for json");
+        static_assert(!reads_view<legacy_base>::value, "from_json() for json");
+        static_assert(!reads_view<unconstrained>::value, "unconstrained from_json()");
+
+        static_assert(nlohmann::is_json_view<json_view>::value, "is_json_view");
+        static_assert(nlohmann::is_json_view<nlohmann::ordered_json_editable_view>::value, "is_json_view");
+        static_assert(!nlohmann::is_json_view<json>::value, "is_json_view");
+        static_assert(!nlohmann::is_json_view<json_document>::value, "is_json_view");
+        static_assert(!nlohmann::is_json_view<int>::value, "is_json_view");
+    }
+
+    SECTION("the library's own conversions are not called with a view (and the probe compiles for them)")
+    {
+        // these go through materialize() (vectors, maps with string keys,
+        // strings, and numbers are converted by the view itself)
+        static_assert(!reads_view<std::list<int>>::value, "std types");
+        static_assert(!reads_view<std::deque<point>>::value, "std types");
+        static_assert(!reads_view<std::set<std::string>>::value, "std types");
+        static_assert(!reads_view<std::unordered_set<int>>::value, "std types");
+        static_assert(!reads_view<std::forward_list<int>>::value, "std types");
+        static_assert(!reads_view<std::valarray<double>>::value, "std types");
+        static_assert(!reads_view<std::array<int, 3>>::value, "std types");
+        static_assert(!reads_view<std::pair<int, std::string>>::value, "std types");
+        static_assert(!reads_view<std::tuple<int, bool, point>>::value, "std types");
+        static_assert(!reads_view<std::map<int, int>>::value, "std types");
+        static_assert(!reads_view<std::unordered_map<int, point>>::value, "std types");
+        static_assert(!reads_view<std::map<color, int>>::value, "std types");
+        static_assert(!reads_view<std::map<std::string, int>>::value, "std types");
+        static_assert(!reads_view<std::vector<point>>::value, "std types");
+        static_assert(!reads_view<std::vector<bool>>::value, "std types");
+        static_assert(!reads_view<std::vector<std::uint8_t>>::value, "std types");
+        static_assert(!reads_view<std::string>::value, "std types");
+        static_assert(!reads_view<int>::value, "std types");
+        static_assert(!reads_view<bool>::value, "std types");
+        static_assert(!reads_view<double>::value, "std types");
+        static_assert(!reads_view<std::nullptr_t>::value, "std types");
+        static_assert(!reads_view<json>::value, "std types");
+        static_assert(!reads_view<json::binary_t>::value, "std types");
+#ifdef JSON_HAS_CPP_17
+        static_assert(!reads_view<std::optional<point>>::value, "std types");
+#endif
+        CHECK(true);
+    }
+
+    SECTION("macro types")
+    {
+        const json_document d = json_document::parse(R"({"name": "s", "points": [{"x": 1, "y": 2}, {"x": 3, "y": 4}],
+            "center": {"x": 5, "y": 6}, "named": {"a": {"x": 7, "y": 8}}})");
+        const shape s = d.root().get<shape>();
+        CHECK(s.name == "s");
+        CHECK(s.points.size() == 2);
+        CHECK(s.points[1].y == 4);
+        CHECK(s.center.x == 5);
+        CHECK(s.named.at("a").y == 8);
+
+        point p;
+        d.root()["center"].get_to(p);
+        CHECK(p.x == 5);
+        CHECK(p.y == 6);
+
+        static_cast<void>(d.root()["center"].get<empty>());
+    }
+
+    SECTION("defaults and names")
+    {
+        const json_document d = json_document::parse(R"({"a": 5, "Value": 3, "Text": "t"})");
+        const with_defaults w = d.root().get<with_defaults>();
+        CHECK(w.a == 5);
+        CHECK(w.b == "default");
+        CHECK(w.c == std::vector<int> {1, 2});
+        const json_document null_document = json_document::parse("null");
+        CHECK(null_document.root().get<with_defaults>().a == 1);
+        const with_names n = d.root().get<with_names>();
+        CHECK(n.value == 3);
+        CHECK(n.text == "t");
+    }
+
+    SECTION("enums")
+    {
+        const json_document d = json_document::parse(R"(["green", null, "purple", 1, "red"])");
+        CHECK(d.root()[0].get<color>() == color::green);
+        CHECK(d.root()[1].get<color>() == color::blue);
+        CHECK(d.root()[2].get<color>() == color::red); // unknown values map to the first entry
+        CHECK(d.root()[3].get<strict_color>() == strict_color::green);
+        CHECK(d.root()[4].get<strict_color>() == strict_color::red);
+#if !defined(JSON_NOEXCEPTION)
+        const json j = d.root().materialize();
+        CHECK(exception_of_call([&] { static_cast<void>(d.root()[2].get<strict_color>()); }) == "[json.exception.out_of_range.410] enum value out of range for strict_color: \"purple\"");
+#if !JSON_DIAGNOSTICS
+        CHECK(exception_of_call([&] { static_cast<void>(d.root()[2].get<strict_color>()); }) == exception_of_call([&] { static_cast<void>(j[2].get<strict_color>()); }));
+#endif
+#endif
+    }
+
+    SECTION("derived types")
+    {
+        const json_document d = json_document::parse(R"({"id": 7, "c": "green", "extra": 3})");
+        const derived x = d.root().get<derived>();
+        CHECK(x.id == 7);
+        CHECK(x.c == color::green);
+        const derived_with_defaults y = d.root().get<derived_with_defaults>();
+        CHECK(y.id == 7);
+        CHECK(y.label == "none");
+        const derived_from_legacy z = d.root().get<derived_from_legacy>();
+        CHECK(z.id == 7);
+        CHECK(z.extra == 3);
+    }
+
+    SECTION("other from_json() functions get the value of materialize()")
+    {
+        const json_document d = json_document::parse(R"({"v": 4})");
+        CHECK(d.root().get<legacy>().v == 4);
+        CHECK(d.root().get<unconstrained>().v == 4);
+        CHECK(d.root().get<constrained>().v == 4);
+        legacy l;
+        d.root().get_to(l);
+        CHECK(l.v == 4);
+    }
+
+    SECTION("duplicate keys: members are looked up in the view, where the first one wins")
+    {
+        const json_document d = json_document::parse(R"({"x": 1, "y": 2, "x": 3})");
+        CHECK(d.root().get<point>().x == 1);
+        // materialize() keeps the last value, like parse()
+        CHECK(d.root().materialize().get<point>().x == 3);
+    }
+
+    SECTION("editable documents and ordered_json")
+    {
+        json_editable_document e = json_editable_document::parse(R"({"x": 1, "y": 2})");
+        e.set(e.root(), "x", 10);
+        CHECK(e.root().get<point>().x == 10);
+        const ordered_json_document o = ordered_json_document::parse(R"({"name": "o", "points": [], "center": {"x": 1, "y": 2}, "named": {}})");
+        CHECK(o.root().get<shape>().center.y == 2);
+    }
+
+#if !defined(JSON_NOEXCEPTION) && !JSON_DIAGNOSTICS
+    SECTION("errors are those of the same conversion of a json value")
+    {
+        // (with JSON_DIAGNOSTICS, those of json name the path of the value)
+        const json_document d = json_document::parse(R"([{"x": 1}, {"x": "1", "y": 2}, [1, 2], {"id": "7", "c": "red"}])");
+        const json j = d.root().materialize();
+        for (std::size_t i = 0; i < 3; ++i)
+        {
+            CAPTURE(i)
+            CHECK(exception_of_call([&] { static_cast<void>(d.root()[i].get<point>()); }) == exception_of_call([&] { static_cast<void>(j[i].get<point>()); }));
+        }
+        CHECK(exception_of_call([&] { static_cast<void>(d.root()[3].get<derived>()); }) == exception_of_call([&] { static_cast<void>(j[3].get<derived>()); }));
+    }
+#endif
+}

tests/src/unit-json_view_image.cpp

@@ -28,11 +28,25 @@ using nlohmann::detail::view::node;
 #include <random>
 #include <sstream>
 #include <string>
+#include <type_traits>
 #include <utility>
 #include <vector>
 
 #include <test_data.hpp>
 
+namespace json_view_image_test
+{
+// whether a document type has save() and load() (only on little-endian targets)
+template<typename T, typename = void>
+struct has_save : std::false_type {};
+template<typename T>
+struct has_save<T, decltype(static_cast<void>(std::declval<const T&>().save()))> : std::true_type {};
+template<typename T, typename = void>
+struct has_load : std::false_type {};
+template<typename T>
+struct has_load<T, decltype(static_cast<void>(T::load(std::declval<const std::vector<std::uint8_t>&>())))> : std::true_type {};
+} // namespace json_view_image_test
+
 #if !(defined(__BYTE_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
 
 namespace
@@ -171,6 +185,9 @@ std::uint32_t rng()
 
 TEST_CASE("json_view images: round trips")
 {
+    static_assert(json_view_image_test::has_save<json_document>::value && json_view_image_test::has_load<json_document>::value, "save() and load() on a little-endian target");
+    static_assert(json_view_image_test::has_save<ordered_json_editable_document>::value && json_view_image_test::has_load<ordered_json_editable_document>::value, "save() and load() on a little-endian target");
+
     SECTION("small documents")
     {
         for (const char* text :
@@ -1275,8 +1292,12 @@ TEST_CASE("json_view images: damaged images")
 
 TEST_CASE("json_view images: big-endian targets")
 {
+    // the image format is little-endian: save() and load() do not exist here
+    static_assert(!json_view_image_test::has_save<json_document>::value, "no save() on a big-endian target");
+    static_assert(!json_view_image_test::has_load<json_document>::value, "no load() on a big-endian target");
+    static_assert(!json_view_image_test::has_save<json_editable_document>::value, "no save() on a big-endian target");
     const json_document d = json_document::parse("[1]");
-    CHECK_THROWS_WITH_AS(d.save(), "[json.exception.type_error.320] json_document images need a little-endian target", json::type_error&);
+    CHECK(d.root().size() == 1);
 }
 
 #endif

tools/generate_natvis/README.md

@@ -34,11 +34,11 @@ version other than the one in `abi_macros.hpp`.
 | Option            | Description                                                                                                                                                                                                                                         |
 |-------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | `--list-tags`     | Print every ABI tag (in namespace order) with the macro that enables it and the `NLOHMANN_JSON_ABI_TAG_*` identifier, then exit.                                                                                                                    |
-| `--abi-tags TAGS` | Add the namespaces of one configuration, given as a comma-separated list of ABI tags (`_diag,_dp,_vns`; the leading underscore is optional, and the order does not matter). Can be repeated for several configurations. Unknown tags are an error. |
+| `--abi-tags TAGS` | Add the namespaces of one configuration, given as a comma-separated list of ABI tags (`_diag,_dp,_ns`; the leading underscore is optional, and the order does not matter). Can be repeated for several configurations. Unknown tags are an error. |
 | `--all`           | Generate the namespaces for every combination of ABI tags. The file size doubles with each tag (about 60 MB for 12 tags). Cannot be combined with `--abi-tags`.                                                                                    |
 | `--output FILE`   | Write the Natvis file to `FILE` instead of `nlohmann_json.natvis` in the repository root.                                                                                                                                                           |
 
-Each configuration gets both the versioned (`json_abi_diag_dp_vns_v3_12_0`) and the unversioned (`json_abi_diag_dp_vns`,
+Each configuration gets both the versioned (`json_abi_diag_dp_ns_v3_12_0`) and the unversioned (`json_abi_diag_dp_ns`,
 used with `NLOHMANN_JSON_NAMESPACE_NO_VERSION`) namespace. The default namespaces (up to two ABI tags) are always
 included, so a generated file can replace the checked-in one.
 
@@ -52,10 +52,10 @@ included, so a generated file can replace the checked-in one.
    ```
 
 3. Generate a Natvis file with them, for example for `JSON_DIAGNOSTICS`, `JSON_DIAGNOSTIC_POSITIONS`, and
-   `JSON_VIEW_NO_SIMD`:
+   `JSON_NO_SIMD`:
 
    ```shell
-   make natvis NATVIS_ARGS="--abi-tags _diag,_dp,_vns --output my_nlohmann_json.natvis"
+   make natvis NATVIS_ARGS="--abi-tags _diag,_dp,_ns --output my_nlohmann_json.natvis"
    ```
 
 4. Use `my_nlohmann_json.natvis` instead of the shipped `nlohmann_json.natvis`, for example by adding it to your Visual

tools/generate_natvis/generate_natvis.py

@@ -91,7 +91,7 @@ if __name__ == '__main__':
                               'include/nlohmann/detail/abi_macros.hpp below "repo_root")')
     selection = parser.add_mutually_exclusive_group()
     selection.add_argument('--abi-tags', action='append', default=[], metavar='TAGS',
-                           help='Comma-separated list of ABI tags (e.g. "_diag,_dp,_vns", leading underscores are '
+                           help='Comma-separated list of ABI tags (e.g. "_diag,_dp,_ns", leading underscores are '
                                 'optional) of one configuration to add to the default namespaces; can be repeated')
     selection.add_argument('--all', action='store_true',
                            help='Generate the namespaces for every combination of ABI tags; the file size doubles '