Guard optional assignment test behind JSON_USE_IMPLICIT_CONVERSIONS

opt_assign = j_null relies on basic_json's implicit conversion
operator to satisfy std::optional's assignment operator template
(which requires is_assignable, not just is_constructible). With
implicit conversions disabled the operator is explicit, so the
assignment doesn't compile at all rather than throwing at runtime.
Fixes the ci_test_noimplicitconversions failure on #5269.

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

docs/mkdocs/docs/api/basic_json/accept.md

@@ -8,8 +8,8 @@ static bool accept(InputType&& i,
                    const bool ignore_trailing_commas = false);
 
 // (2)
-template<typename IteratorType, typename SentinelType = IteratorType>
-static bool accept(IteratorType first, SentinelType last,
+template<typename IteratorType>
+static bool accept(IteratorType first, IteratorType last,
                    const bool ignore_comments = false,
                    const bool ignore_trailing_commas = false);
 ```
@@ -17,11 +17,10 @@ static bool accept(IteratorType first, SentinelType last,
 Checks whether the input is valid JSON.
 
 1. Reads from a compatible input.
-2. Reads from a pair of character iterators, or an iterator and a sentinel of a different type (C++20 ranges support)
+2. Reads from a pair of character iterators
     
     The value_type of the iterator must be an integral type with a size of 1, 2, or 4 bytes, which will be interpreted
-    respectively as UTF-8, UTF-16, and UTF-32. If `SentinelType` differs from `IteratorType`, it must be comparable to
-    the iterator type with `operator!=`.
+    respectively as UTF-8, UTF-16, and UTF-32.
     
 Unlike the [`parse()`](parse.md) function, this function neither throws an exception in case of invalid JSON input
 (i.e., a parse error) nor creates diagnostic information.
@@ -45,12 +44,6 @@ Unlike the [`parse()`](parse.md) function, this function neither throws an excep
     - a pair of `std::string::iterator` or `std::vector<std::uint8_t>::iterator`
     - a pair of pointers such as `ptr` and `ptr + len`
 
-`SentinelType`
-:   defaults to `IteratorType`; may be a different type comparable to `IteratorType` via `operator!=`, for instance.
-
-    - a custom sentinel type for C++20 ranges
-    - `std::counted_iterator` with a different sentinel type
-
 ## Parameters
 
 `i` (in)
@@ -68,7 +61,7 @@ Unlike the [`parse()`](parse.md) function, this function neither throws an excep
 :   iterator to the start of the character range
 
 `last` (in)
-:   iterator to the end of the character range, or a sentinel value that compares equal to the end iterator with `operator!=`
+:   iterator to the end of the character range
 
 ## Return value
 
@@ -119,7 +112,6 @@ A UTF-8 byte order mark is silently ignored.
 - Changed [runtime assertion](../../features/assertions.md) in case of `FILE*` null pointers to exception in version 3.12.0.
 - Added `ignore_trailing_commas` in version 3.13.0.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
-- Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
 
 !!! warning "Deprecation"
 

docs/mkdocs/docs/api/basic_json/binary_t.md

@@ -51,38 +51,6 @@ represent a byte array in modern C++.
 
 The default values for `BinaryType` is `#!cpp std::vector<std::uint8_t>`.
 
-#### Custom BinaryType behavior
-
-When a custom `BinaryType` is configured (other than the default `#!cpp std::vector<std::uint8_t>`), you can assign
-values of that type directly to a `basic_json` instance, and they will automatically be recognized as binary values
-rather than arrays:
-
-```cpp
-using custom_json = nlohmann::basic_json<
-    nlohmann::ordered_map,  // ObjectType
-    std::vector,            // ArrayType
-    std::string,            // StringType
-    bool,                   // BooleanType
-    std::int64_t,           // NumberIntegerType
-    std::uint64_t,          // NumberUnsignedType
-    double,                 // NumberFloatType
-    std::allocator,         // AllocatorType
-    nlohmann::adl_serializer,
-    std::vector<std::byte>  // Custom BinaryType
->;
-
-std::vector<std::byte> data{std::byte{1}, std::byte{2}, std::byte{3}};
-custom_json j = data;  // Creates a binary value, not an array
-assert(j.is_binary());
-
-// Round-tripping works seamlessly
-auto extracted = j.get<std::vector<std::byte>>();
-assert(extracted == data);
-```
-
-This automatic type detection is a convenience feature that only applies to custom (non-default) `BinaryType` configurations.
-The default `nlohmann::json` continues to treat `#!cpp std::vector<std::uint8_t>` as arrays for backward compatibility.
-
 #### Storage
 
 Binary Arrays are stored as pointers in a `basic_json` type. That is, for any access to array values, a pointer of the

docs/mkdocs/docs/api/basic_json/from_bjdata.md

@@ -7,8 +7,8 @@ static basic_json from_bjdata(InputType&& i,
                               const bool strict = true,
                               const bool allow_exceptions = true);
 // (2)
-template<typename IteratorType, typename SentinelType = IteratorType>
-static basic_json from_bjdata(IteratorType first, SentinelType last,
+template<typename IteratorType>
+static basic_json from_bjdata(IteratorType first, IteratorType last,
                               const bool strict = true,
                               const bool allow_exceptions = true);
 ```
@@ -16,7 +16,7 @@ static basic_json from_bjdata(IteratorType first, SentinelType last,
 Deserializes a given input to a JSON value using the BJData (Binary JData) serialization format.
 
 1. Reads from a compatible input.
-2. Reads from an iterator range, or an iterator and a sentinel of a different type (C++20 ranges support).
+2. Reads from an iterator range.
 
 The exact mapping and its limitations are described on a [dedicated page](../../features/binary_formats/bjdata.md).
 
@@ -35,10 +35,6 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 `IteratorType`
 :   a compatible iterator type
 
-`SentinelType`
-:   defaults to `IteratorType`; may be a different type comparable to `IteratorType` via `operator!=`, for instance a
-    custom sentinel type for C++20 ranges
-
 ## Parameters
 
 `i` (in)
@@ -48,7 +44,7 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 :   iterator to the start of the input
 
 `last` (in)
-:   iterator to the end of the input, or a sentinel value that compares equal to the end iterator with `operator!=`
+:   iterator to the end of the input
 
 `strict` (in)
 :   whether to expect the input to be consumed until EOF (`#!cpp true` by default)
@@ -107,4 +103,3 @@ Linear in the size of the input.
 
 - Added in version 3.11.0.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
-- Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.

docs/mkdocs/docs/api/basic_json/from_bson.md

@@ -7,8 +7,8 @@ static basic_json from_bson(InputType&& i,
                             const bool strict = true,
                             const bool allow_exceptions = true);
 // (2)
-template<typename IteratorType, typename SentinelType = IteratorType>
-static basic_json from_bson(IteratorType first, SentinelType last,
+template<typename IteratorType>
+static basic_json from_bson(IteratorType first, IteratorType last,
                             const bool strict = true,
                             const bool allow_exceptions = true);
 ```
@@ -16,7 +16,7 @@ static basic_json from_bson(IteratorType first, SentinelType last,
 Deserializes a given input to a JSON value using the BSON (Binary JSON) serialization format.
 
 1. Reads from a compatible input.
-2. Reads from an iterator range, or an iterator and a sentinel of a different type (C++20 ranges support).
+2. Reads from an iterator range.
 
 The exact mapping and its limitations are described on a [dedicated page](../../features/binary_formats/bson.md).
 
@@ -35,10 +35,6 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 `IteratorType`
 :   a compatible iterator type
 
-`SentinelType`
-:   defaults to `IteratorType`; may be a different type comparable to `IteratorType` via `operator!=`, for instance a
-    custom sentinel type for C++20 ranges
-
 ## Parameters
 
 `i` (in)
@@ -48,7 +44,7 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 :   iterator to the start of the input
 
 `last` (in)
-:   iterator to the end of the input, or a sentinel value that compares equal to the end iterator with `operator!=`
+:   iterator to the end of the input
 
 `strict` (in)
 :   whether to expect the input to be consumed until EOF (`#!cpp true` by default)
@@ -107,7 +103,6 @@ Linear in the size of the input.
 
 - Added in version 3.4.0.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
-- Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
 
 !!! warning "Deprecation"
 

docs/mkdocs/docs/api/basic_json/from_cbor.md

@@ -9,8 +9,8 @@ static basic_json from_cbor(InputType&& i,
                             const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error);
 
 // (2)
-template<typename IteratorType, typename SentinelType = IteratorType>
-static basic_json from_cbor(IteratorType first, SentinelType last,
+template<typename IteratorType>
+static basic_json from_cbor(IteratorType first, IteratorType last,
                             const bool strict = true,
                             const bool allow_exceptions = true,
                             const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error);
@@ -19,7 +19,7 @@ static basic_json from_cbor(IteratorType first, SentinelType last,
 Deserializes a given input to a JSON value using the CBOR (Concise Binary Object Representation) serialization format.
 
 1. Reads from a compatible input.
-2. Reads from an iterator range, or an iterator and a sentinel of a different type (C++20 ranges support).
+2. Reads from an iterator range.
 
 The exact mapping and its limitations are described on a [dedicated page](../../features/binary_formats/cbor.md).
 
@@ -38,10 +38,6 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 `IteratorType`
 :   a compatible iterator type
 
-`SentinelType`
-:   defaults to `IteratorType`; may be a different type comparable to `IteratorType` via `operator!=`, for instance a
-    custom sentinel type for C++20 ranges
-
 ## Parameters
 
 `i` (in)
@@ -51,7 +47,7 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 :   iterator to the start of the input
 
 `last` (in)
-:   iterator to the end of the input, or a sentinel value that compares equal to the end iterator with `operator!=`
+:   iterator to the end of the input
 
 `strict` (in)
 :   whether to expect the input to be consumed until EOF (`#!cpp true` by default)
@@ -117,7 +113,6 @@ Linear in the size of the input.
 - Added `allow_exceptions` parameter in version 3.2.0.
 - Added `tag_handler` parameter in version 3.9.0.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
-- Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
 
 !!! warning "Deprecation"
 

docs/mkdocs/docs/api/basic_json/from_msgpack.md

@@ -7,8 +7,8 @@ static basic_json from_msgpack(InputType&& i,
                                const bool strict = true,
                                const bool allow_exceptions = true);
 // (2)
-template<typename IteratorType, typename SentinelType = IteratorType>
-static basic_json from_msgpack(IteratorType first, SentinelType last,
+template<typename IteratorType>
+static basic_json from_msgpack(IteratorType first, IteratorType last,
                                const bool strict = true,
                                const bool allow_exceptions = true);
 ```
@@ -16,7 +16,7 @@ static basic_json from_msgpack(IteratorType first, SentinelType last,
 Deserializes a given input to a JSON value using the MessagePack serialization format.
 
 1. Reads from a compatible input.
-2. Reads from an iterator range, or an iterator and a sentinel of a different type (C++20 ranges support).
+2. Reads from an iterator range.
 
 The exact mapping and its limitations are described on a [dedicated page](../../features/binary_formats/messagepack.md).
 
@@ -35,10 +35,6 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 `IteratorType`
 :   a compatible iterator type
 
-`SentinelType`
-:   defaults to `IteratorType`; may be a different type comparable to `IteratorType` via `operator!=`, for instance a
-    custom sentinel type for C++20 ranges
-
 ## Parameters
 
 `i` (in)
@@ -48,7 +44,7 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 :   iterator to the start of the input
 
 `last` (in)
-:   iterator to the end of the input, or a sentinel value that compares equal to the end iterator with `operator!=`
+:   iterator to the end of the input
 
 `strict` (in)
 :   whether to expect the input to be consumed until EOF (`#!cpp true` by default)
@@ -109,7 +105,6 @@ Linear in the size of the input.
 - Changed to consume input adapters, removed `start_index` parameter, and added `strict` parameter in version 3.0.0.
 - Added `allow_exceptions` parameter in version 3.2.0.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
-- Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
 
 !!! warning "Deprecation"
 

docs/mkdocs/docs/api/basic_json/from_ubjson.md

@@ -7,8 +7,8 @@ static basic_json from_ubjson(InputType&& i,
                               const bool strict = true,
                               const bool allow_exceptions = true);
 // (2)
-template<typename IteratorType, typename SentinelType = IteratorType>
-static basic_json from_ubjson(IteratorType first, SentinelType last,
+template<typename IteratorType>
+static basic_json from_ubjson(IteratorType first, IteratorType last,
                               const bool strict = true,
                               const bool allow_exceptions = true);
 ```
@@ -16,7 +16,7 @@ static basic_json from_ubjson(IteratorType first, SentinelType last,
 Deserializes a given input to a JSON value using the UBJSON (Universal Binary JSON) serialization format.
 
 1. Reads from a compatible input.
-2. Reads from an iterator range, or an iterator and a sentinel of a different type (C++20 ranges support).
+2. Reads from an iterator range.
 
 The exact mapping and its limitations are described on a [dedicated page](../../features/binary_formats/ubjson.md).
 
@@ -35,10 +35,6 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 `IteratorType`
 :   a compatible iterator type
 
-`SentinelType`
-:   defaults to `IteratorType`; may be a different type comparable to `IteratorType` via `operator!=`, for instance a
-    custom sentinel type for C++20 ranges
-
 ## Parameters
 
 `i` (in)
@@ -48,7 +44,7 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 :   iterator to the start of the input
 
 `last` (in)
-:   iterator to the end of the input, or a sentinel value that compares equal to the end iterator with `operator!=`
+:   iterator to the end of the input
 
 `strict` (in)
 :   whether to expect the input to be consumed until EOF (`#!cpp true` by default)
@@ -108,7 +104,6 @@ Linear in the size of the input.
 - Added in version 3.1.0.
 - Added `allow_exceptions` parameter in version 3.2.0.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
-- Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
 
 !!! warning "Deprecation"
 

docs/mkdocs/docs/api/basic_json/parse.md

@@ -10,8 +10,8 @@ static basic_json parse(InputType&& i,
                         const bool ignore_trailing_commas = false);
 
 // (2)
-template<typename IteratorType, typename SentinelType = IteratorType>
-static basic_json parse(IteratorType first, SentinelType last,
+template<typename IteratorType>
+static basic_json parse(IteratorType first, IteratorType last,
                         const parser_callback_t cb = nullptr,
                         const bool allow_exceptions = true,
                         const bool ignore_comments = false,
@@ -19,11 +19,10 @@ static basic_json parse(IteratorType first, SentinelType last,
 ```
 
 1. Deserialize from a compatible input.
-2. Deserialize from a pair of character iterators, or an iterator and a sentinel of a different type (C++20 ranges support)
+2. Deserialize from a pair of character iterators
     
     The `value_type` of the iterator must be an integral type with size of 1, 2, or 4 bytes, which will be interpreted
-    respectively as UTF-8, UTF-16, and UTF-32. If `SentinelType` differs from `IteratorType`, it must be comparable to
-    the iterator type with `operator!=`.
+    respectively as UTF-8, UTF-16, and UTF-32.
 
 ## Template parameters
 
@@ -44,12 +43,6 @@ static basic_json parse(IteratorType first, SentinelType last,
     - a pair of `std::string::iterator` or `std::vector<std::uint8_t>::iterator`
     - a pair of pointers such as `ptr` and `ptr + len`
 
-`SentinelType`
-:   defaults to `IteratorType`; may be a different type comparable to `IteratorType` via `operator!=`, for instance.
-
-    - a custom sentinel type for C++20 ranges
-    - `std::counted_iterator` with a different sentinel type
-
 ## Parameters
 
 `i` (in)
@@ -74,7 +67,7 @@ static basic_json parse(IteratorType first, SentinelType last,
 :   iterator to the start of a character range
 
 `last` (in)
-:   iterator to the end of a character range, or a sentinel value that compares equal to the end iterator with `operator!=`
+:   iterator to the end of a character range
 
 ## Return value
 
@@ -245,7 +238,6 @@ Invalid Unicode escapes and unpaired surrogates in the input are reported as
 - Changed [runtime assertion](../../features/assertions.md) in case of `FILE*` null pointers to exception in version 3.12.0.
 - Added `ignore_trailing_commas` in version 3.13.0.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
-- Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
 
 !!! warning "Deprecation"
 

docs/mkdocs/docs/api/basic_json/sax_parse.md

@@ -11,8 +11,8 @@ static bool sax_parse(InputType&& i,
                       const bool ignore_trailing_commas = false);
 
 // (2)
-template<class IteratorType, class SAX, class SentinelType = IteratorType>
-static bool sax_parse(IteratorType first, SentinelType last,
+template<class IteratorType, class SAX>
+static bool sax_parse(IteratorType first, IteratorType last,
                       SAX* sax,
                       input_format_t format = input_format_t::json,
                       const bool strict = true,
@@ -23,11 +23,10 @@ static bool sax_parse(IteratorType first, SentinelType last,
 Read from input and generate SAX events
 
 1. Read from a compatible input.
-2. Read from a pair of character iterators, or an iterator and a sentinel of a different type (C++20 ranges support)
+2. Read from a pair of character iterators
     
     The value_type of the iterator must be an integral type with a size of 1, 2, or 4 bytes, which will be interpreted
-    respectively as UTF-8, UTF-16, and UTF-32. If `SentinelType` differs from `IteratorType`, it must be comparable to
-    the iterator type with `operator!=`.
+    respectively as UTF-8, UTF-16, and UTF-32.
 
 The SAX event lister must follow the interface of [`json_sax`](../json_sax/index.md).
 
@@ -47,9 +46,6 @@ The SAX event lister must follow the interface of [`json_sax`](../json_sax/index
 :   a compatible iterator type for overload (2); a pair of character iterators whose `value_type` is an integral type
     with a size of 1, 2, or 4 bytes (interpreted respectively as UTF-8, UTF-16, and UTF-32)
 
-`SentinelType`
-:   defaults to `IteratorType`; may be a different type comparable to `IteratorType` via `operator!=`, for overload (2)
-
 `SAX`
 :   a class fulfilling the SAX event listener interface; see [`json_sax`](../json_sax/index.md)
 
@@ -80,7 +76,7 @@ The SAX event lister must follow the interface of [`json_sax`](../json_sax/index
 :   iterator to the start of a character range
 
 `last` (in)
-:   iterator to the end of a character range, or a sentinel value that compares equal to the end iterator with `operator!=`
+:   iterator to the end of a character range
 
 ## Return value
 
@@ -132,7 +128,6 @@ A UTF-8 byte order mark is silently ignored.
 - Ignoring comments via `ignore_comments` added in version 3.9.0.
 - Added `ignore_trailing_commas` in version 3.13.0.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
-- Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
 
 !!! warning "Deprecation"
 

docs/mkdocs/docs/api/macros/json_diagnostics.md

@@ -38,8 +38,7 @@ When the macro is not defined, the library will define it to its default value.
 
     Diagnostic messages can also be controlled with the CMake option
     [`JSON_Diagnostics`](../../integration/cmake.md#json_diagnostics) (`OFF` by default)
-    which defines `JSON_DIAGNOSTICS` accordingly. Note this only applies when building the
-    library from source — see the pre-installed-package caveat on that page.
+    which defines `JSON_DIAGNOSTICS` accordingly.
 
 ## Examples
 

docs/mkdocs/docs/features/conversions.md

@@ -47,28 +47,6 @@ json j = {{"one", 1}, {"two", 2}};
 auto m = j.get<std::map<std::string, int>>();  // {{"one", 1}, {"two", 2}}
 ```
 
-`#!cpp std::pair` and `#!cpp std::tuple` are also supported, converting positionally to and from a JSON array:
-
-```cpp
-json j = {1.0, "hello", 42};
-auto t = j.get<std::tuple<double, std::string, int>>();  // {1.0, "hello", 42}
-```
-
-!!! info "Extracting references into a tuple"
-
-    A tuple type may also hold references (e.g. `#!cpp std::tuple<double&, std::string&>`) to avoid copying: `get`
-    then returns a tuple of references pointing directly at the elements stored inside the `basic_json` array,
-    rather than a tuple of copies:
-
-    ```cpp
-    json j = {1.0, "hello"};
-    auto refs = j.get<std::tuple<double&, std::string&>>();
-    std::get<1>(refs) = "world";  // modifies j[1] in place
-    ```
-
-    A referenced type must be one the library actually stores (or an arithmetic type it can convert to/from);
-    otherwise this is a compile error.
-
 ## Implicit conversions
 
 By default, a JSON value implicitly converts to a compatible C++ type, so the explicit `get` call can often be omitted:
@@ -158,20 +136,6 @@ std::vector<int> numbers = {1, 2, 3};
 json j = numbers;   // [1,2,3]
 ```
 
-!!! info "Constructing from a C++20 range view"
-
-    A `json` array can also be constructed directly from a C++20 range view (`std::ranges::view`), such as the result
-    of `std::views::filter` or `std::views::transform` -- no intermediate container is needed:
-
-    ```cpp
-    std::vector<int> nums{1, 2, 37, 42, 21};
-    auto filtered = nums | std::views::filter([](int i) { return i > 10; });
-    json j(filtered);   // [37,42,21]
-    ```
-
-    This requires [`JSON_HAS_RANGES`](../api/macros/json_has_ranges.md) to be enabled and is unavailable on MinGW due
-    to incomplete C++20 ranges support there.
-
 ## Your own types
 
 The conversions above are built in for standard types. To make the same syntax work for **your own** types, provide

docs/mkdocs/docs/integration/cmake.md

@@ -135,31 +135,6 @@ Enable CI build targets. The exact targets are used during the several CI steps
 
 Enable [extended diagnostic messages](../home/exceptions.md#extended-diagnostic-messages) by defining macro [`JSON_DIAGNOSTICS`](../api/macros/json_diagnostics.md). This option is `OFF` by default.
 
-!!! warning "Does not apply to a pre-installed package"
-
-    This option only takes effect when building nlohmann/json from source as part of your own
-    CMake project (e.g. via [`FetchContent`](#fetchcontent) or [`add_subdirectory`](#external)).
-    It has **no effect** on a package that was already built and installed elsewhere (Homebrew,
-    vcpkg, a system package, etc.) — the resulting compile definition is baked into the exported
-    `nlohmann_jsonTargets.cmake` at install time, and `set(JSON_Diagnostics ON)` before
-    `find_package()` does not change it (verified against the Homebrew-installed package: the
-    exported target still carries a fixed `$<$<BOOL:OFF>:JSON_DIAGNOSTICS=1>`, regardless of any
-    variable set in the consuming project).
-
-    To enable extended diagnostics for a pre-installed package, override the imported target's
-    property directly after `find_package()`:
-
-    ```cmake
-    find_package(nlohmann_json REQUIRED)
-    set_target_properties(nlohmann_json::nlohmann_json PROPERTIES
-        INTERFACE_COMPILE_DEFINITIONS "JSON_DIAGNOSTICS=1")
-    ```
-
-    This only works cleanly when your project is the sole consumer of that imported target. If
-    nlohmann_json is pulled in from more than one place in your dependency graph with different
-    `JSON_DIAGNOSTICS` values, you may see a `"JSON_DIAGNOSTICS" redefined` compiler error, since
-    conflicting `-D` flags can end up on the same compile command line.
-
 ### `JSON_Diagnostic_Positions`
 
 Enable position diagnostics by defining macro [`JSON_DIAGNOSTIC_POSITIONS`](../api/macros/json_diagnostic_positions.md). This option is `OFF` by default.

include/nlohmann/detail/conversions/from_json.hpp

@@ -19,7 +19,6 @@
 #include <unordered_map> // unordered_map
 #include <utility> // pair, declval
 #include <valarray> // valarray
-#include <vector> // vector
 
 #include <nlohmann/detail/exceptions.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
@@ -333,7 +332,6 @@ template < typename BasicJsonType, typename ConstructibleArrayType,
                !is_constructible_object_type<BasicJsonType, ConstructibleArrayType>::value&&
                !is_constructible_string_type<BasicJsonType, ConstructibleArrayType>::value&&
                !std::is_same<ConstructibleArrayType, typename BasicJsonType::binary_t>::value&&
-               !is_compatible_binary_type<BasicJsonType, ConstructibleArrayType>::value&&
                !is_basic_json<ConstructibleArrayType>::value,
                int > = 0 >
 auto from_json(const BasicJsonType& j, ConstructibleArrayType& arr)
@@ -379,25 +377,6 @@ inline void from_json(const BasicJsonType& j, typename BasicJsonType::binary_t&
     bin = *j.template get_ptr<const typename BasicJsonType::binary_t*>();
 }
 
-template < typename BasicJsonType, typename CompatibleArrayType,
-           enable_if_t < is_compatible_binary_type<BasicJsonType, CompatibleArrayType>::value,
-                         int > = 0 >
-inline void from_json(const BasicJsonType& j, CompatibleArrayType& bin)
-{
-    if (j.is_binary())
-    {
-        bin = static_cast<CompatibleArrayType>(*j.template get_ptr<const typename BasicJsonType::binary_t*>());
-    }
-    else if (j.is_array())
-    {
-        from_json_array_impl(j, bin, priority_tag<3> {});
-    }
-    else
-    {
-        JSON_THROW(type_error::create(302, concat("type must be binary or array, but is ", j.type_name()), &j));
-    }
-}
-
 template<typename BasicJsonType, typename ConstructibleObjectType,
          enable_if_t<is_constructible_object_type<BasicJsonType, ConstructibleObjectType>::value, int> = 0>
 inline void from_json(const BasicJsonType& j, ConstructibleObjectType& obj)

include/nlohmann/detail/conversions/to_json.hpp

@@ -377,7 +377,6 @@ template < typename BasicJsonType, typename CompatibleArrayType,
                          !is_compatible_object_type<BasicJsonType, CompatibleArrayType>::value&&
                          !is_compatible_string_type<BasicJsonType, CompatibleArrayType>::value&&
                          !std::is_same<typename BasicJsonType::binary_t, CompatibleArrayType>::value&&
-                         !is_compatible_binary_type<BasicJsonType, CompatibleArrayType>::value&&
                          !is_basic_json<CompatibleArrayType>::value
 #if JSON_HAS_RANGES && !defined(__MINGW32__)
     && !is_compatible_range_view<CompatibleArrayType>::value
@@ -407,14 +406,6 @@ inline void to_json(BasicJsonType& j, const typename BasicJsonType::binary_t& bi
     external_constructor<value_t::binary>::construct(j, bin);
 }
 
-template < typename BasicJsonType, typename CompatibleArrayType,
-           enable_if_t < is_compatible_binary_type<BasicJsonType, CompatibleArrayType>::value,
-                         int > = 0 >
-inline void to_json(BasicJsonType& j, const CompatibleArrayType& bin)
-{
-    external_constructor<value_t::binary>::construct(j, typename BasicJsonType::binary_t(bin));
-}
-
 template<typename BasicJsonType, typename T,
          enable_if_t<std::is_convertible<T, BasicJsonType>::value, int> = 0>
 inline void to_json(BasicJsonType& j, const std::valarray<T>& arr)

include/nlohmann/detail/input/input_adapters.hpp

@@ -155,9 +155,7 @@ class input_stream_adapter
 
 // General-purpose iterator-based adapter. It might not be as fast as
 // theoretically possible for some containers, but it is extremely versatile.
-// SentinelType defaults to IteratorType for backward compatibility, but may
-// be a different type (e.g., a C++20 sentinel or counted_iterator).
-template<typename IteratorType, typename SentinelType = IteratorType>
+template<typename IteratorType>
 class iterator_input_adapter
 {
   public:
@@ -171,10 +169,9 @@ class iterator_input_adapter
     // in wide_string_input_adapter, which does not expose this).
     static constexpr bool supports_seek =
         std::is_same<typename std::iterator_traits<IteratorType>::iterator_category, std::random_access_iterator_tag>::value
-        && std::is_same<IteratorType, SentinelType>::value
         && sizeof(char_type) == 1;
 
-    iterator_input_adapter(IteratorType first, SentinelType last)
+    iterator_input_adapter(IteratorType first, IteratorType last)
         : begin(first), current(std::move(first)), end(std::move(last))
     {}
 
@@ -219,14 +216,12 @@ class iterator_input_adapter
   private:
     // whether IteratorType refers to a contiguous range and therefore supports
     // a std::memcpy fast path (pointers always do; in C++20 we can also detect
-    // library iterators such as those of std::vector and std::string).
-    // The fast path also requires SentinelType == IteratorType so std::distance works.
+    // library iterators such as those of std::vector and std::string)
     static constexpr bool iterator_is_contiguous =
-        std::is_same<IteratorType, SentinelType>::value && (
 #if defined(__cpp_lib_concepts) && defined(JSON_HAS_CPP_20)
-            std::contiguous_iterator<IteratorType> ||
+        std::contiguous_iterator<IteratorType> ||
 #endif
-            std::is_pointer<IteratorType>::value);
+        std::is_pointer<IteratorType>::value;
 
     // contiguous fast path: bulk copy the remaining range with std::memcpy
     template<class T>
@@ -272,7 +267,7 @@ class iterator_input_adapter
 
     IteratorType begin;
     IteratorType current;
-    SentinelType end;
+    IteratorType end;
 
     template<typename BaseInputAdapter, size_t T>
     friend struct wide_string_input_helper;
@@ -458,54 +453,19 @@ class wide_string_input_adapter
     std::size_t utf8_bytes_filled = 0;
 };
 
-template<typename IteratorType, typename SentinelType = IteratorType, typename Enable = void>
+template<typename IteratorType, typename Enable = void>
 struct iterator_input_adapter_factory
 {
     using iterator_type = IteratorType;
-    using sentinel_type = SentinelType;
     using char_type = typename std::iterator_traits<iterator_type>::value_type;
-    using adapter_type = iterator_input_adapter<iterator_type, sentinel_type>;
+    using adapter_type = iterator_input_adapter<iterator_type>;
 
-    static adapter_type create(IteratorType first, SentinelType last)
+    static adapter_type create(IteratorType first, IteratorType last)
     {
         return adapter_type(std::move(first), std::move(last));
     }
 };
 
-// Detection: whether IteratorType and SentinelType can be compared with !=
-template<typename IteratorType, typename SentinelType, typename = void>
-struct can_compare_ne_impl : std::false_type {};
-
-template<typename IteratorType, typename SentinelType>
-struct can_compare_ne_impl < IteratorType, SentinelType,
-       void_t < decltype(std::declval<IteratorType>() != std::declval<SentinelType>()) >>
-           : std::true_type {};
-
-// Workaround for reversed operator order
-template<typename IteratorType, typename SentinelType, typename = void>
-struct can_compare_ne_reversed : std::false_type {};
-
-template<typename IteratorType, typename SentinelType>
-struct can_compare_ne_reversed < IteratorType, SentinelType,
-       void_t < decltype(std::declval<SentinelType>() != std::declval<IteratorType>()) >>
-           : std::true_type {};
-
-template<typename IteratorType, typename SentinelType>
-struct can_compare_ne_either_order : std::integral_constant < bool,
-    can_compare_ne_impl<IteratorType, SentinelType>::value ||
-    can_compare_ne_reversed<IteratorType, SentinelType>::value > {};
-
-// std::nullptr_t is excluded explicitly: a literal `nullptr` passed as a
-// trailing default argument (e.g. parse(s, nullptr, ...)) must never be
-// mistaken for a sentinel, and some compilers (e.g. GCC 4.8) unreliably
-// SFINAE the `operator!=` detection above for std::nullptr_t against
-// container/string types, which would otherwise make such calls ambiguous
-// with the compatible-input overload.
-template<typename IteratorType, typename SentinelType>
-struct can_compare_ne : std::integral_constant < bool,
-    !std::is_same<SentinelType, std::nullptr_t>::value &&
-    can_compare_ne_either_order<IteratorType, SentinelType>::value > {};
-
 template<typename T>
 struct is_iterator_of_multibyte
 {
@@ -516,31 +476,25 @@ struct is_iterator_of_multibyte
     };
 };
 
-template<typename IteratorType, typename SentinelType>
-struct iterator_input_adapter_factory<IteratorType, SentinelType, enable_if_t<is_iterator_of_multibyte<IteratorType>::value>>
+template<typename IteratorType>
+struct iterator_input_adapter_factory<IteratorType, enable_if_t<is_iterator_of_multibyte<IteratorType>::value>>
 {
     using iterator_type = IteratorType;
-    using sentinel_type = SentinelType;
     using char_type = typename std::iterator_traits<iterator_type>::value_type;
-    using base_adapter_type = iterator_input_adapter<iterator_type, sentinel_type>;
+    using base_adapter_type = iterator_input_adapter<iterator_type>;
     using adapter_type = wide_string_input_adapter<base_adapter_type, char_type>;
 
-    static adapter_type create(IteratorType first, SentinelType last)
+    static adapter_type create(IteratorType first, IteratorType last)
     {
         return adapter_type(base_adapter_type(std::move(first), std::move(last)));
     }
 };
 
-// General purpose iterator-based input (iterator+sentinel pair; SentinelType
-// defaults to IteratorType for the common same-type case, but may differ for
-// C++20 ranges-style iterator+sentinel pairs). Only enable for types that can
-// be compared with !=.
-template < typename IteratorType, typename SentinelType = IteratorType,
-           typename = typename std::enable_if <
-               can_compare_ne<IteratorType, SentinelType>::value >::type >
-typename iterator_input_adapter_factory<IteratorType, SentinelType>::adapter_type input_adapter(IteratorType first, SentinelType last)
+// General purpose iterator-based input
+template<typename IteratorType>
+typename iterator_input_adapter_factory<IteratorType>::adapter_type input_adapter(IteratorType first, IteratorType last)
 {
-    using factory_type = iterator_input_adapter_factory<IteratorType, SentinelType>;
+    using factory_type = iterator_input_adapter_factory<IteratorType>;
     return factory_type::create(first, last);
 }
 

include/nlohmann/detail/meta/type_traits.hpp

@@ -13,7 +13,6 @@
 #include <tuple> // tuple
 #include <type_traits> // false_type, is_constructible, is_integral, is_same, true_type
 #include <utility> // declval
-#include <vector> // vector
 #if defined(__cpp_lib_byte) && __cpp_lib_byte >= 201603L
     #include <cstddef> // byte
 #endif
@@ -633,14 +632,6 @@ template<typename BasicJsonType, typename CompatibleType>
 struct is_compatible_type
     : is_compatible_type_impl<BasicJsonType, CompatibleType> {};
 
-template<typename BasicJsonType, typename CompatibleArrayType>
-struct is_compatible_binary_type
-{
-    static constexpr bool value =
-        std::is_same<typename BasicJsonType::binary_t::container_type, CompatibleArrayType>::value &&
-        !std::is_same<typename BasicJsonType::binary_t::container_type, std::vector<std::uint8_t>>::value;
-};
-
 template<typename BasicJsonType, typename CompatibleReferenceType>
 struct is_compatible_reference_type_impl
 {

include/nlohmann/json.hpp

@@ -4083,13 +4083,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return result;
     }
 
-    /// @brief deserialize from a pair of character iterators (or an iterator+sentinel pair, C++20 ranges support)
+    /// @brief deserialize from a pair of character iterators
     /// @sa https://json.nlohmann.me/api/basic_json/parse/
-    template<typename IteratorType, typename SentinelType = IteratorType,
-             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
+    template<typename IteratorType>
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json parse(IteratorType first,
-                            SentinelType last,
+                            IteratorType last,
                             parser_callback_t cb = nullptr,
                             const bool allow_exceptions = true,
                             const bool ignore_comments = false,
@@ -4123,11 +4122,10 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return parser(detail::input_adapter(std::forward<InputType>(i)), nullptr, false, ignore_comments, ignore_trailing_commas).accept(true);
     }
 
-    /// @brief check if the input is valid JSON (iterator pair, or iterator+sentinel pair for C++20 ranges support)
+    /// @brief check if the input is valid JSON
     /// @sa https://json.nlohmann.me/api/basic_json/accept/
-    template<typename IteratorType, typename SentinelType = IteratorType,
-             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
-    static bool accept(IteratorType first, SentinelType last,
+    template<typename IteratorType>
+    static bool accept(IteratorType first, IteratorType last,
                        const bool ignore_comments = false,
                        const bool ignore_trailing_commas = false)
     {
@@ -4159,12 +4157,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                : detail::binary_reader<basic_json, decltype(ia), SAX>(std::move(ia), format).sax_parse(format, sax, strict);
     }
 
-    /// @brief generate SAX events (iterator pair, or iterator+sentinel pair for C++20 ranges support)
+    /// @brief generate SAX events
     /// @sa https://json.nlohmann.me/api/basic_json/sax_parse/
-    template<class IteratorType, class SAX, class SentinelType = IteratorType,
-             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
+    template<class IteratorType, class SAX>
     JSON_HEDLEY_NON_NULL(3)
-    static bool sax_parse(IteratorType first, SentinelType last, SAX* sax,
+    static bool sax_parse(IteratorType first, IteratorType last, SAX* sax,
                           input_format_t format = input_format_t::json,
                           const bool strict = true,
                           const bool ignore_comments = false,
@@ -4464,12 +4461,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
-    /// @brief create a JSON value from an input in CBOR format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
+    /// @brief create a JSON value from an input in CBOR format
     /// @sa https://json.nlohmann.me/api/basic_json/from_cbor/
-    template<typename IteratorType, typename SentinelType = IteratorType,
-             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
+    template<typename IteratorType>
     JSON_HEDLEY_WARN_UNUSED_RESULT
-    static basic_json from_cbor(IteratorType first, SentinelType last,
+    static basic_json from_cbor(IteratorType first, IteratorType last,
                                 const bool strict = true,
                                 const bool allow_exceptions = true,
                                 const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error)
@@ -4522,12 +4518,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
-    /// @brief create a JSON value from an input in MessagePack format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
+    /// @brief create a JSON value from an input in MessagePack format
     /// @sa https://json.nlohmann.me/api/basic_json/from_msgpack/
-    template<typename IteratorType, typename SentinelType = IteratorType,
-             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
+    template<typename IteratorType>
     JSON_HEDLEY_WARN_UNUSED_RESULT
-    static basic_json from_msgpack(IteratorType first, SentinelType last,
+    static basic_json from_msgpack(IteratorType first, IteratorType last,
                                    const bool strict = true,
                                    const bool allow_exceptions = true)
     {
@@ -4577,12 +4572,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
-    /// @brief create a JSON value from an input in UBJSON format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
+    /// @brief create a JSON value from an input in UBJSON format
     /// @sa https://json.nlohmann.me/api/basic_json/from_ubjson/
-    template<typename IteratorType, typename SentinelType = IteratorType,
-             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
+    template<typename IteratorType>
     JSON_HEDLEY_WARN_UNUSED_RESULT
-    static basic_json from_ubjson(IteratorType first, SentinelType last,
+    static basic_json from_ubjson(IteratorType first, IteratorType last,
                                   const bool strict = true,
                                   const bool allow_exceptions = true)
     {
@@ -4632,12 +4626,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
-    /// @brief create a JSON value from an input in BJData format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
+    /// @brief create a JSON value from an input in BJData format
     /// @sa https://json.nlohmann.me/api/basic_json/from_bjdata/
-    template<typename IteratorType, typename SentinelType = IteratorType,
-             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
+    template<typename IteratorType>
     JSON_HEDLEY_WARN_UNUSED_RESULT
-    static basic_json from_bjdata(IteratorType first, SentinelType last,
+    static basic_json from_bjdata(IteratorType first, IteratorType last,
                                   const bool strict = true,
                                   const bool allow_exceptions = true)
     {
@@ -4663,12 +4656,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
-    /// @brief create a JSON value from an input in BSON format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
+    /// @brief create a JSON value from an input in BSON format
     /// @sa https://json.nlohmann.me/api/basic_json/from_bson/
-    template<typename IteratorType, typename SentinelType = IteratorType,
-             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
+    template<typename IteratorType>
     JSON_HEDLEY_WARN_UNUSED_RESULT
-    static basic_json from_bson(IteratorType first, SentinelType last,
+    static basic_json from_bson(IteratorType first, IteratorType last,
                                 const bool strict = true,
                                 const bool allow_exceptions = true)
     {

single_include/nlohmann/json.hpp

@@ -189,7 +189,6 @@
 #include <unordered_map> // unordered_map
 #include <utility> // pair, declval
 #include <valarray> // valarray
-#include <vector> // vector
 
 // #include <nlohmann/detail/exceptions.hpp>
 //     __ _____ _____ _____
@@ -3593,7 +3592,6 @@ NLOHMANN_JSON_NAMESPACE_END
 #include <tuple> // tuple
 #include <type_traits> // false_type, is_constructible, is_integral, is_same, true_type
 #include <utility> // declval
-#include <vector> // vector
 #if defined(__cpp_lib_byte) && __cpp_lib_byte >= 201603L
     #include <cstddef> // byte
 #endif
@@ -4396,14 +4394,6 @@ template<typename BasicJsonType, typename CompatibleType>
 struct is_compatible_type
     : is_compatible_type_impl<BasicJsonType, CompatibleType> {};
 
-template<typename BasicJsonType, typename CompatibleArrayType>
-struct is_compatible_binary_type
-{
-    static constexpr bool value =
-        std::is_same<typename BasicJsonType::binary_t::container_type, CompatibleArrayType>::value &&
-        !std::is_same<typename BasicJsonType::binary_t::container_type, std::vector<std::uint8_t>>::value;
-};
-
 template<typename BasicJsonType, typename CompatibleReferenceType>
 struct is_compatible_reference_type_impl
 {
@@ -5547,7 +5537,6 @@ template < typename BasicJsonType, typename ConstructibleArrayType,
                !is_constructible_object_type<BasicJsonType, ConstructibleArrayType>::value&&
                !is_constructible_string_type<BasicJsonType, ConstructibleArrayType>::value&&
                !std::is_same<ConstructibleArrayType, typename BasicJsonType::binary_t>::value&&
-               !is_compatible_binary_type<BasicJsonType, ConstructibleArrayType>::value&&
                !is_basic_json<ConstructibleArrayType>::value,
                int > = 0 >
 auto from_json(const BasicJsonType& j, ConstructibleArrayType& arr)
@@ -5593,25 +5582,6 @@ inline void from_json(const BasicJsonType& j, typename BasicJsonType::binary_t&
     bin = *j.template get_ptr<const typename BasicJsonType::binary_t*>();
 }
 
-template < typename BasicJsonType, typename CompatibleArrayType,
-           enable_if_t < is_compatible_binary_type<BasicJsonType, CompatibleArrayType>::value,
-                         int > = 0 >
-inline void from_json(const BasicJsonType& j, CompatibleArrayType& bin)
-{
-    if (j.is_binary())
-    {
-        bin = static_cast<CompatibleArrayType>(*j.template get_ptr<const typename BasicJsonType::binary_t*>());
-    }
-    else if (j.is_array())
-    {
-        from_json_array_impl(j, bin, priority_tag<3> {});
-    }
-    else
-    {
-        JSON_THROW(type_error::create(302, concat("type must be binary or array, but is ", j.type_name()), &j));
-    }
-}
-
 template<typename BasicJsonType, typename ConstructibleObjectType,
          enable_if_t<is_constructible_object_type<BasicJsonType, ConstructibleObjectType>::value, int> = 0>
 inline void from_json(const BasicJsonType& j, ConstructibleObjectType& obj)
@@ -6508,7 +6478,6 @@ template < typename BasicJsonType, typename CompatibleArrayType,
                          !is_compatible_object_type<BasicJsonType, CompatibleArrayType>::value&&
                          !is_compatible_string_type<BasicJsonType, CompatibleArrayType>::value&&
                          !std::is_same<typename BasicJsonType::binary_t, CompatibleArrayType>::value&&
-                         !is_compatible_binary_type<BasicJsonType, CompatibleArrayType>::value&&
                          !is_basic_json<CompatibleArrayType>::value
 #if JSON_HAS_RANGES && !defined(__MINGW32__)
     && !is_compatible_range_view<CompatibleArrayType>::value
@@ -6538,14 +6507,6 @@ inline void to_json(BasicJsonType& j, const typename BasicJsonType::binary_t& bi
     external_constructor<value_t::binary>::construct(j, bin);
 }
 
-template < typename BasicJsonType, typename CompatibleArrayType,
-           enable_if_t < is_compatible_binary_type<BasicJsonType, CompatibleArrayType>::value,
-                         int > = 0 >
-inline void to_json(BasicJsonType& j, const CompatibleArrayType& bin)
-{
-    external_constructor<value_t::binary>::construct(j, typename BasicJsonType::binary_t(bin));
-}
-
 template<typename BasicJsonType, typename T,
          enable_if_t<std::is_convertible<T, BasicJsonType>::value, int> = 0>
 inline void to_json(BasicJsonType& j, const std::valarray<T>& arr)
@@ -7142,9 +7103,7 @@ class input_stream_adapter
 
 // General-purpose iterator-based adapter. It might not be as fast as
 // theoretically possible for some containers, but it is extremely versatile.
-// SentinelType defaults to IteratorType for backward compatibility, but may
-// be a different type (e.g., a C++20 sentinel or counted_iterator).
-template<typename IteratorType, typename SentinelType = IteratorType>
+template<typename IteratorType>
 class iterator_input_adapter
 {
   public:
@@ -7158,10 +7117,9 @@ class iterator_input_adapter
     // in wide_string_input_adapter, which does not expose this).
     static constexpr bool supports_seek =
         std::is_same<typename std::iterator_traits<IteratorType>::iterator_category, std::random_access_iterator_tag>::value
-        && std::is_same<IteratorType, SentinelType>::value
         && sizeof(char_type) == 1;
 
-    iterator_input_adapter(IteratorType first, SentinelType last)
+    iterator_input_adapter(IteratorType first, IteratorType last)
         : begin(first), current(std::move(first)), end(std::move(last))
     {}
 
@@ -7206,14 +7164,12 @@ class iterator_input_adapter
   private:
     // whether IteratorType refers to a contiguous range and therefore supports
     // a std::memcpy fast path (pointers always do; in C++20 we can also detect
-    // library iterators such as those of std::vector and std::string).
-    // The fast path also requires SentinelType == IteratorType so std::distance works.
+    // library iterators such as those of std::vector and std::string)
     static constexpr bool iterator_is_contiguous =
-        std::is_same<IteratorType, SentinelType>::value && (
 #if defined(__cpp_lib_concepts) && defined(JSON_HAS_CPP_20)
-            std::contiguous_iterator<IteratorType> ||
+        std::contiguous_iterator<IteratorType> ||
 #endif
-            std::is_pointer<IteratorType>::value);
+        std::is_pointer<IteratorType>::value;
 
     // contiguous fast path: bulk copy the remaining range with std::memcpy
     template<class T>
@@ -7259,7 +7215,7 @@ class iterator_input_adapter
 
     IteratorType begin;
     IteratorType current;
-    SentinelType end;
+    IteratorType end;
 
     template<typename BaseInputAdapter, size_t T>
     friend struct wide_string_input_helper;
@@ -7445,54 +7401,19 @@ class wide_string_input_adapter
     std::size_t utf8_bytes_filled = 0;
 };
 
-template<typename IteratorType, typename SentinelType = IteratorType, typename Enable = void>
+template<typename IteratorType, typename Enable = void>
 struct iterator_input_adapter_factory
 {
     using iterator_type = IteratorType;
-    using sentinel_type = SentinelType;
     using char_type = typename std::iterator_traits<iterator_type>::value_type;
-    using adapter_type = iterator_input_adapter<iterator_type, sentinel_type>;
+    using adapter_type = iterator_input_adapter<iterator_type>;
 
-    static adapter_type create(IteratorType first, SentinelType last)
+    static adapter_type create(IteratorType first, IteratorType last)
     {
         return adapter_type(std::move(first), std::move(last));
     }
 };
 
-// Detection: whether IteratorType and SentinelType can be compared with !=
-template<typename IteratorType, typename SentinelType, typename = void>
-struct can_compare_ne_impl : std::false_type {};
-
-template<typename IteratorType, typename SentinelType>
-struct can_compare_ne_impl < IteratorType, SentinelType,
-       void_t < decltype(std::declval<IteratorType>() != std::declval<SentinelType>()) >>
-           : std::true_type {};
-
-// Workaround for reversed operator order
-template<typename IteratorType, typename SentinelType, typename = void>
-struct can_compare_ne_reversed : std::false_type {};
-
-template<typename IteratorType, typename SentinelType>
-struct can_compare_ne_reversed < IteratorType, SentinelType,
-       void_t < decltype(std::declval<SentinelType>() != std::declval<IteratorType>()) >>
-           : std::true_type {};
-
-template<typename IteratorType, typename SentinelType>
-struct can_compare_ne_either_order : std::integral_constant < bool,
-    can_compare_ne_impl<IteratorType, SentinelType>::value ||
-    can_compare_ne_reversed<IteratorType, SentinelType>::value > {};
-
-// std::nullptr_t is excluded explicitly: a literal `nullptr` passed as a
-// trailing default argument (e.g. parse(s, nullptr, ...)) must never be
-// mistaken for a sentinel, and some compilers (e.g. GCC 4.8) unreliably
-// SFINAE the `operator!=` detection above for std::nullptr_t against
-// container/string types, which would otherwise make such calls ambiguous
-// with the compatible-input overload.
-template<typename IteratorType, typename SentinelType>
-struct can_compare_ne : std::integral_constant < bool,
-    !std::is_same<SentinelType, std::nullptr_t>::value &&
-    can_compare_ne_either_order<IteratorType, SentinelType>::value > {};
-
 template<typename T>
 struct is_iterator_of_multibyte
 {
@@ -7503,31 +7424,25 @@ struct is_iterator_of_multibyte
     };
 };
 
-template<typename IteratorType, typename SentinelType>
-struct iterator_input_adapter_factory<IteratorType, SentinelType, enable_if_t<is_iterator_of_multibyte<IteratorType>::value>>
+template<typename IteratorType>
+struct iterator_input_adapter_factory<IteratorType, enable_if_t<is_iterator_of_multibyte<IteratorType>::value>>
 {
     using iterator_type = IteratorType;
-    using sentinel_type = SentinelType;
     using char_type = typename std::iterator_traits<iterator_type>::value_type;
-    using base_adapter_type = iterator_input_adapter<iterator_type, sentinel_type>;
+    using base_adapter_type = iterator_input_adapter<iterator_type>;
     using adapter_type = wide_string_input_adapter<base_adapter_type, char_type>;
 
-    static adapter_type create(IteratorType first, SentinelType last)
+    static adapter_type create(IteratorType first, IteratorType last)
     {
         return adapter_type(base_adapter_type(std::move(first), std::move(last)));
     }
 };
 
-// General purpose iterator-based input (iterator+sentinel pair; SentinelType
-// defaults to IteratorType for the common same-type case, but may differ for
-// C++20 ranges-style iterator+sentinel pairs). Only enable for types that can
-// be compared with !=.
-template < typename IteratorType, typename SentinelType = IteratorType,
-           typename = typename std::enable_if <
-               can_compare_ne<IteratorType, SentinelType>::value >::type >
-typename iterator_input_adapter_factory<IteratorType, SentinelType>::adapter_type input_adapter(IteratorType first, SentinelType last)
+// General purpose iterator-based input
+template<typename IteratorType>
+typename iterator_input_adapter_factory<IteratorType>::adapter_type input_adapter(IteratorType first, IteratorType last)
 {
-    using factory_type = iterator_input_adapter_factory<IteratorType, SentinelType>;
+    using factory_type = iterator_input_adapter_factory<IteratorType>;
     return factory_type::create(first, last);
 }
 
@@ -25130,13 +25045,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return result;
     }
 
-    /// @brief deserialize from a pair of character iterators (or an iterator+sentinel pair, C++20 ranges support)
+    /// @brief deserialize from a pair of character iterators
     /// @sa https://json.nlohmann.me/api/basic_json/parse/
-    template<typename IteratorType, typename SentinelType = IteratorType,
-             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
+    template<typename IteratorType>
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json parse(IteratorType first,
-                            SentinelType last,
+                            IteratorType last,
                             parser_callback_t cb = nullptr,
                             const bool allow_exceptions = true,
                             const bool ignore_comments = false,
@@ -25170,11 +25084,10 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return parser(detail::input_adapter(std::forward<InputType>(i)), nullptr, false, ignore_comments, ignore_trailing_commas).accept(true);
     }
 
-    /// @brief check if the input is valid JSON (iterator pair, or iterator+sentinel pair for C++20 ranges support)
+    /// @brief check if the input is valid JSON
     /// @sa https://json.nlohmann.me/api/basic_json/accept/
-    template<typename IteratorType, typename SentinelType = IteratorType,
-             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
-    static bool accept(IteratorType first, SentinelType last,
+    template<typename IteratorType>
+    static bool accept(IteratorType first, IteratorType last,
                        const bool ignore_comments = false,
                        const bool ignore_trailing_commas = false)
     {
@@ -25206,12 +25119,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                : detail::binary_reader<basic_json, decltype(ia), SAX>(std::move(ia), format).sax_parse(format, sax, strict);
     }
 
-    /// @brief generate SAX events (iterator pair, or iterator+sentinel pair for C++20 ranges support)
+    /// @brief generate SAX events
     /// @sa https://json.nlohmann.me/api/basic_json/sax_parse/
-    template<class IteratorType, class SAX, class SentinelType = IteratorType,
-             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
+    template<class IteratorType, class SAX>
     JSON_HEDLEY_NON_NULL(3)
-    static bool sax_parse(IteratorType first, SentinelType last, SAX* sax,
+    static bool sax_parse(IteratorType first, IteratorType last, SAX* sax,
                           input_format_t format = input_format_t::json,
                           const bool strict = true,
                           const bool ignore_comments = false,
@@ -25511,12 +25423,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
-    /// @brief create a JSON value from an input in CBOR format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
+    /// @brief create a JSON value from an input in CBOR format
     /// @sa https://json.nlohmann.me/api/basic_json/from_cbor/
-    template<typename IteratorType, typename SentinelType = IteratorType,
-             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
+    template<typename IteratorType>
     JSON_HEDLEY_WARN_UNUSED_RESULT
-    static basic_json from_cbor(IteratorType first, SentinelType last,
+    static basic_json from_cbor(IteratorType first, IteratorType last,
                                 const bool strict = true,
                                 const bool allow_exceptions = true,
                                 const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error)
@@ -25569,12 +25480,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
-    /// @brief create a JSON value from an input in MessagePack format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
+    /// @brief create a JSON value from an input in MessagePack format
     /// @sa https://json.nlohmann.me/api/basic_json/from_msgpack/
-    template<typename IteratorType, typename SentinelType = IteratorType,
-             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
+    template<typename IteratorType>
     JSON_HEDLEY_WARN_UNUSED_RESULT
-    static basic_json from_msgpack(IteratorType first, SentinelType last,
+    static basic_json from_msgpack(IteratorType first, IteratorType last,
                                    const bool strict = true,
                                    const bool allow_exceptions = true)
     {
@@ -25624,12 +25534,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
-    /// @brief create a JSON value from an input in UBJSON format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
+    /// @brief create a JSON value from an input in UBJSON format
     /// @sa https://json.nlohmann.me/api/basic_json/from_ubjson/
-    template<typename IteratorType, typename SentinelType = IteratorType,
-             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
+    template<typename IteratorType>
     JSON_HEDLEY_WARN_UNUSED_RESULT
-    static basic_json from_ubjson(IteratorType first, SentinelType last,
+    static basic_json from_ubjson(IteratorType first, IteratorType last,
                                   const bool strict = true,
                                   const bool allow_exceptions = true)
     {
@@ -25679,12 +25588,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
-    /// @brief create a JSON value from an input in BJData format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
+    /// @brief create a JSON value from an input in BJData format
     /// @sa https://json.nlohmann.me/api/basic_json/from_bjdata/
-    template<typename IteratorType, typename SentinelType = IteratorType,
-             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
+    template<typename IteratorType>
     JSON_HEDLEY_WARN_UNUSED_RESULT
-    static basic_json from_bjdata(IteratorType first, SentinelType last,
+    static basic_json from_bjdata(IteratorType first, IteratorType last,
                                   const bool strict = true,
                                   const bool allow_exceptions = true)
     {
@@ -25710,12 +25618,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return res ? result : basic_json(value_t::discarded);
     }
 
-    /// @brief create a JSON value from an input in BSON format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
+    /// @brief create a JSON value from an input in BSON format
     /// @sa https://json.nlohmann.me/api/basic_json/from_bson/
-    template<typename IteratorType, typename SentinelType = IteratorType,
-             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
+    template<typename IteratorType>
     JSON_HEDLEY_WARN_UNUSED_RESULT
-    static basic_json from_bson(IteratorType first, SentinelType last,
+    static basic_json from_bson(IteratorType first, IteratorType last,
                                 const bool strict = true,
                                 const bool allow_exceptions = true)
     {

tests/src/test_utils.hpp

@@ -30,17 +30,4 @@ inline std::vector<std::uint8_t> read_binary_file(const std::string& filename)
     return byte_vector;
 }
 
-// sentinel for istreambuf_iterator; compares != true until EOF is reached
-// lets tests read a file directly via the new iterator+sentinel overloads
-// instead of buffering the whole file into a vector first.
-// Only the iterator-first direction (it != sentinel) is ever evaluated by
-// the library's parse loop, so no reversed-order overload is needed.
-struct istreambuf_sentinel
-{
-    friend bool operator!=(const std::istreambuf_iterator<char>& it, const istreambuf_sentinel& /*unused*/) noexcept
-    {
-        return it != std::istreambuf_iterator<char>();
-    }
-};
-
 } // namespace utils

tests/src/unit-bjdata.cpp

@@ -3699,15 +3699,6 @@ TEST_CASE("Universal Binary JSON Specification Examples 1")
     }
 }
 
-TEST_CASE("Parse BJData directly from a file using iterator and sentinel")
-{
-    std::string const filename = TEST_DATA_DIRECTORY "/json_testsuite/sample.json.bjdata";
-    std::ifstream file(filename, std::ios::binary);
-    const std::istreambuf_iterator<char> first(file);
-    const json parsed = json::from_bjdata(first, utils::istreambuf_sentinel{});
-    CHECK((parsed.is_object() || parsed.is_array()));
-}
-
 #if !defined(JSON_NOEXCEPTION)
 TEST_CASE("all BJData first bytes")
 {

tests/src/unit-bson.cpp

@@ -1208,19 +1208,6 @@ TEST_CASE("BSON numerical data")
     }
 }
 
-TEST_CASE("Parse BSON directly from a file using iterator and sentinel")
-{
-    std::string const filename = TEST_DATA_DIRECTORY "/json.org/1.json";
-
-    std::ifstream f_json(filename);
-    const json expected = json::parse(f_json);
-
-    std::ifstream file(filename + ".bson", std::ios::binary);
-    const std::istreambuf_iterator<char> first(file);
-    const json parsed = json::from_bson(first, utils::istreambuf_sentinel{});
-    CHECK(parsed == expected);
-}
-
 TEST_CASE("BSON roundtrips" * doctest::skip())
 {
     SECTION("reference files")

tests/src/unit-cbor.cpp

@@ -1921,15 +1921,6 @@ TEST_CASE("single CBOR roundtrip")
     }
 }
 
-TEST_CASE("Parse CBOR directly from a file using iterator and sentinel")
-{
-    std::string const filename = TEST_DATA_DIRECTORY "/json_testsuite/sample.json.cbor";
-    std::ifstream file(filename, std::ios::binary);
-    const std::istreambuf_iterator<char> first(file);
-    const json parsed = json::from_cbor(first, utils::istreambuf_sentinel{});
-    CHECK((parsed.is_object() || parsed.is_array()));
-}
-
 #if !defined(JSON_NOEXCEPTION)
 TEST_CASE("CBOR regressions")
 {

tests/src/unit-conversions.cpp

@@ -1782,6 +1782,21 @@ TEST_CASE("std::optional")
                              "[json.exception.type_error.302] type must be string, but is null", json::type_error&);
         CHECK_THROWS_WITH_AS(std::optional<int>(j_null),
                              "[json.exception.type_error.302] type must be number, but is null", json::type_error&);
+
+        // Assignment goes through the same overload resolution as direct
+        // construction, so it throws for the same reason. This relies on
+        // basic_json's implicit conversion operator, so it only applies
+        // when JSON_USE_IMPLICIT_CONVERSIONS is enabled (the default).
+#if JSON_USE_IMPLICIT_CONVERSIONS
+        std::optional<std::string> opt_assign;
+        CHECK_THROWS_WITH_AS(opt_assign = j_null,
+                             "[json.exception.type_error.302] type must be string, but is null", json::type_error&);
+#endif
+
+        // get_to() is the correct way to obtain std::nullopt from a JSON null.
+        std::optional<std::string> opt_get_to = "placeholder";
+        j_null.get_to(opt_get_to);
+        CHECK(opt_get_to == std::nullopt);
     }
 
     SECTION("string")

tests/src/unit-msgpack.cpp

@@ -1641,15 +1641,6 @@ TEST_CASE("single MessagePack roundtrip")
     }
 }
 
-TEST_CASE("Parse MessagePack directly from a file using iterator and sentinel")
-{
-    std::string const filename = TEST_DATA_DIRECTORY "/json_testsuite/sample.json.msgpack";
-    std::ifstream file(filename, std::ios::binary);
-    const std::istreambuf_iterator<char> first(file);
-    const json parsed = json::from_msgpack(first, utils::istreambuf_sentinel{});
-    CHECK((parsed.is_object() || parsed.is_array()));
-}
-
 TEST_CASE("MessagePack roundtrips" * doctest::skip())
 {
     SECTION("input from msgpack-python")

tests/src/unit-regression2.cpp

@@ -1136,40 +1136,6 @@ TEST_CASE("regression tests 2")
         CHECK((decoded == json_4804::array()));
     }
 
-    SECTION("discussion #4209 - custom BinaryType direct assignment and round-tripping")
-    {
-        // Test that assigning a custom BinaryType directly creates a binary value, not an array
-        const std::vector<std::byte> original{std::byte{1}, std::byte{2}, std::byte{3}};
-        const json_4804 j = original;
-        CHECK(j.is_binary());
-        CHECK(!j.is_array());
-
-        // Test round-tripping: extracting the binary value back as the custom container type
-        const auto extracted = j.get<std::vector<std::byte>>();
-        CHECK(extracted == original);
-
-        // Test that the default json alias behavior is unchanged: std::vector<uint8_t> -> array
-        const json default_json = std::vector<std::uint8_t> {1, 2, 3};
-        CHECK(default_json.is_array());
-        CHECK(!default_json.is_binary());
-    }
-
-    SECTION("discussion #4209 - custom BinaryType extraction from parsed array")
-    {
-        // Test that extracting a custom BinaryType from a parsed JSON array still works
-        // (not just from a binary-typed node)
-        const auto j = json_4804::parse("[1,2,3]");
-        CHECK(j.is_array());
-        CHECK(!j.is_binary());
-
-        // Extracting as custom BinaryType should work from arrays
-        const auto extracted = j.get<std::vector<std::byte>>();
-        CHECK(extracted.size() == 3);
-        CHECK(extracted[0] == std::byte{1});
-        CHECK(extracted[1] == std::byte{2});
-        CHECK(extracted[2] == std::byte{3});
-    }
-
     SECTION("issue #5046 - implicit conversion of return json to std::optional no longer implicit")
     {
         const json jval{};

tests/src/unit-ubjson.cpp

@@ -2393,15 +2393,6 @@ TEST_CASE("Universal Binary JSON Specification Examples 1")
     }
 }
 
-TEST_CASE("Parse UBJSON directly from a file using iterator and sentinel")
-{
-    std::string const filename = TEST_DATA_DIRECTORY "/json_testsuite/sample.json.ubjson";
-    std::ifstream file(filename, std::ios::binary);
-    const std::istreambuf_iterator<char> first(file);
-    const json parsed = json::from_ubjson(first, utils::istreambuf_sentinel{});
-    CHECK((parsed.is_object() || parsed.is_array()));
-}
-
 #if !defined(JSON_NOEXCEPTION)
 TEST_CASE("all UBJSON first bytes")
 {

tests/src/unit-user_defined_input.cpp

@@ -168,37 +168,4 @@ TEST_CASE("Custom iterator")
     CHECK(as_json.at(3) == 4);
 }
 
-// Custom sentinel type for testing heterogeneous iterator+sentinel support
-struct CustomSentinel
-{
-    const char* end_ptr;
-
-    // only the iterator-first direction (it != sentinel) is ever evaluated by
-    // the library's parse loop; a reversed-order overload would go unused and
-    // trip -Wunneeded-internal-declaration under -Weverything
-    friend bool operator!=(const char* it, const CustomSentinel& sentinel)
-    {
-        return it != sentinel.end_ptr;
-    }
-};
-
-TEST_CASE("Parse with heterogeneous iterator and sentinel types")
-{
-    const std::string json_str = R"({"key":"value"})";
-    const char* end_ptr = json_str.data() + json_str.size();
-
-    // Parse using pointer and sentinel (different types)
-    json j = json::parse(json_str.data(), CustomSentinel{end_ptr});
-    CHECK(j["key"] == "value");
-
-    // Accept using pointer and sentinel
-    CHECK(json::accept(json_str.data(), CustomSentinel{end_ptr}));
-
-    // Test that the same-type case still works
-    std::string raw_data = R"([1,2,3])";
-    std::list<char> data(raw_data.begin(), raw_data.end());
-    json j2 = json::parse(data.begin(), data.end());
-    CHECK(j2.at(0) == 1);
-}
-
 } // namespace