Extend std::optional null regression coverage (assignment, get_to) (#5269)

Both had zero documentation anywhere in docs/mkdocs/. The tuple/pair
gap was first spotted in the very first git-log audit pass but never
turned into an actionable todo, so it persisted uncaught across four
subsequent passes.

- Document basic positional std::pair/std::tuple <-> json array
  conversion, plus #5016's reference-extraction capability
  (get<std::tuple<T&, T&>>() returning references into the stored
  array elements).
- Document #5205's new json-from-C++20-range-view constructor
  (e.g. nums | std::views::filter(...)).

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>
+template<typename IteratorType, typename SentinelType = IteratorType>
-static bool accept(IteratorType first, IteratorType last,
+static bool accept(IteratorType first, SentinelType last,
                    const bool ignore_comments = false,
                    const bool ignore_trailing_commas = false);
 ```
@@ -17,10 +17,11 @@ static bool accept(IteratorType first, IteratorType last,
 Checks whether the input is valid JSON.
 
 1. Reads from a compatible input.
-2. Reads from a pair of character iterators
+2. Reads from a pair of character iterators, or an iterator and a sentinel of a different type (C++20 ranges support)
     
     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.
+    respectively as UTF-8, UTF-16, and UTF-32. If `SentinelType` differs from `IteratorType`, it must be comparable to
+    the iterator type with `operator!=`.
     
 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.
@@ -44,6 +45,12 @@ 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::default_sentinel_t`, when `IteratorType` is `std::counted_iterator`
+
 ## Parameters
 
 `i` (in)
@@ -61,7 +68,7 @@ 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
+:   iterator to the end of the character range, or a sentinel value that compares equal to the end iterator with `operator!=`
 
 ## Return value
 
@@ -112,6 +119,7 @@ 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

@@ -51,6 +51,38 @@ 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>
+template<typename IteratorType, typename SentinelType = IteratorType>
-static basic_json from_bjdata(IteratorType first, IteratorType last,
+static basic_json from_bjdata(IteratorType first, SentinelType last,
                               const bool strict = true,
                               const bool allow_exceptions = true);
 ```
@@ -16,7 +16,7 @@ static basic_json from_bjdata(IteratorType first, IteratorType 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.
+2. Reads from an iterator range, or an iterator and a sentinel of a different type (C++20 ranges support).
 
 The exact mapping and its limitations are described on a [dedicated page](../../features/binary_formats/bjdata.md).
 
@@ -35,6 +35,12 @@ 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
+    - `std::default_sentinel_t`, when `IteratorType` is `std::counted_iterator`
+
 ## Parameters
 
 `i` (in)
@@ -44,7 +50,7 @@ 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
+:   iterator to the end of the input, or a sentinel value that compares equal to the end iterator with `operator!=`
 
 `strict` (in)
 :   whether to expect the input to be consumed until EOF (`#!cpp true` by default)
@@ -103,3 +109,4 @@ 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>
+template<typename IteratorType, typename SentinelType = IteratorType>
-static basic_json from_bson(IteratorType first, IteratorType last,
+static basic_json from_bson(IteratorType first, SentinelType last,
                             const bool strict = true,
                             const bool allow_exceptions = true);
 ```
@@ -16,7 +16,7 @@ static basic_json from_bson(IteratorType first, IteratorType 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.
+2. Reads from an iterator range, or an iterator and a sentinel of a different type (C++20 ranges support).
 
 The exact mapping and its limitations are described on a [dedicated page](../../features/binary_formats/bson.md).
 
@@ -35,6 +35,12 @@ 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
+    - `std::default_sentinel_t`, when `IteratorType` is `std::counted_iterator`
+
 ## Parameters
 
 `i` (in)
@@ -44,7 +50,7 @@ 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
+:   iterator to the end of the input, or a sentinel value that compares equal to the end iterator with `operator!=`
 
 `strict` (in)
 :   whether to expect the input to be consumed until EOF (`#!cpp true` by default)
@@ -103,6 +109,7 @@ 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>
+template<typename IteratorType, typename SentinelType = IteratorType>
-static basic_json from_cbor(IteratorType first, IteratorType last,
+static basic_json from_cbor(IteratorType first, SentinelType 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, IteratorType 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.
+2. Reads from an iterator range, or an iterator and a sentinel of a different type (C++20 ranges support).
 
 The exact mapping and its limitations are described on a [dedicated page](../../features/binary_formats/cbor.md).
 
@@ -38,6 +38,12 @@ 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
+    - `std::default_sentinel_t`, when `IteratorType` is `std::counted_iterator`
+
 ## Parameters
 
 `i` (in)
@@ -47,7 +53,7 @@ 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
+:   iterator to the end of the input, or a sentinel value that compares equal to the end iterator with `operator!=`
 
 `strict` (in)
 :   whether to expect the input to be consumed until EOF (`#!cpp true` by default)
@@ -113,6 +119,7 @@ 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>
+template<typename IteratorType, typename SentinelType = IteratorType>
-static basic_json from_msgpack(IteratorType first, IteratorType last,
+static basic_json from_msgpack(IteratorType first, SentinelType last,
                                const bool strict = true,
                                const bool allow_exceptions = true);
 ```
@@ -16,7 +16,7 @@ static basic_json from_msgpack(IteratorType first, IteratorType 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.
+2. Reads from an iterator range, or an iterator and a sentinel of a different type (C++20 ranges support).
 
 The exact mapping and its limitations are described on a [dedicated page](../../features/binary_formats/messagepack.md).
 
@@ -35,6 +35,12 @@ 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
+    - `std::default_sentinel_t`, when `IteratorType` is `std::counted_iterator`
+
 ## Parameters
 
 `i` (in)
@@ -44,7 +50,7 @@ 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
+:   iterator to the end of the input, or a sentinel value that compares equal to the end iterator with `operator!=`
 
 `strict` (in)
 :   whether to expect the input to be consumed until EOF (`#!cpp true` by default)
@@ -105,6 +111,7 @@ 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>
+template<typename IteratorType, typename SentinelType = IteratorType>
-static basic_json from_ubjson(IteratorType first, IteratorType last,
+static basic_json from_ubjson(IteratorType first, SentinelType last,
                               const bool strict = true,
                               const bool allow_exceptions = true);
 ```
@@ -16,7 +16,7 @@ static basic_json from_ubjson(IteratorType first, IteratorType 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.
+2. Reads from an iterator range, or an iterator and a sentinel of a different type (C++20 ranges support).
 
 The exact mapping and its limitations are described on a [dedicated page](../../features/binary_formats/ubjson.md).
 
@@ -35,6 +35,12 @@ 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
+    - `std::default_sentinel_t`, when `IteratorType` is `std::counted_iterator`
+
 ## Parameters
 
 `i` (in)
@@ -44,7 +50,7 @@ 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
+:   iterator to the end of the input, or a sentinel value that compares equal to the end iterator with `operator!=`
 
 `strict` (in)
 :   whether to expect the input to be consumed until EOF (`#!cpp true` by default)
@@ -104,6 +110,7 @@ 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>
+template<typename IteratorType, typename SentinelType = IteratorType>
-static basic_json parse(IteratorType first, IteratorType last,
+static basic_json parse(IteratorType first, SentinelType last,
                         const parser_callback_t cb = nullptr,
                         const bool allow_exceptions = true,
                         const bool ignore_comments = false,
@@ -19,10 +19,11 @@ static basic_json parse(IteratorType first, IteratorType last,
 ```
 
 1. Deserialize from a compatible input.
-2. Deserialize from a pair of character iterators
+2. Deserialize from a pair of character iterators, or an iterator and a sentinel of a different type (C++20 ranges support)
     
     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.
+    respectively as UTF-8, UTF-16, and UTF-32. If `SentinelType` differs from `IteratorType`, it must be comparable to
+    the iterator type with `operator!=`.
 
 ## Template parameters
 
@@ -43,6 +44,12 @@ static basic_json parse(IteratorType first, IteratorType 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::default_sentinel_t`, when `IteratorType` is `std::counted_iterator`
+
 ## Parameters
 
 `i` (in)
@@ -67,7 +74,7 @@ static basic_json parse(IteratorType first, IteratorType last,
 :   iterator to the start of a character range
 
 `last` (in)
-:   iterator to the end of a character range
+:   iterator to the end of a character range, or a sentinel value that compares equal to the end iterator with `operator!=`
 
 ## Return value
 
@@ -238,6 +245,7 @@ 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>
+template<class IteratorType, class SAX, class SentinelType = IteratorType>
-static bool sax_parse(IteratorType first, IteratorType last,
+static bool sax_parse(IteratorType first, SentinelType last,
                       SAX* sax,
                       input_format_t format = input_format_t::json,
                       const bool strict = true,
@@ -23,10 +23,11 @@ static bool sax_parse(IteratorType first, IteratorType last,
 Read from input and generate SAX events
 
 1. Read from a compatible input.
-2. Read from a pair of character iterators
+2. Read from a pair of character iterators, or an iterator and a sentinel of a different type (C++20 ranges support)
     
     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.
+    respectively as UTF-8, UTF-16, and UTF-32. If `SentinelType` differs from `IteratorType`, it must be comparable to
+    the iterator type with `operator!=`.
 
 The SAX event lister must follow the interface of [`json_sax`](../json_sax/index.md).
 
@@ -46,6 +47,12 @@ 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), for instance.
+
+    - a custom sentinel type for C++20 ranges
+    - `std::default_sentinel_t`, when `IteratorType` is `std::counted_iterator`
+
 `SAX`
 :   a class fulfilling the SAX event listener interface; see [`json_sax`](../json_sax/index.md)
 
@@ -76,7 +83,7 @@ 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
+:   iterator to the end of a character range, or a sentinel value that compares equal to the end iterator with `operator!=`
 
 ## Return value
 
@@ -128,6 +135,7 @@ 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

@@ -38,7 +38,8 @@ 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.
+    which defines `JSON_DIAGNOSTICS` accordingly. Note this only applies when building the
+    library from source — see the pre-installed-package caveat on that page.
 
 ## Examples
 

docs/mkdocs/docs/features/conversions.md

@@ -47,6 +47,28 @@ 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:
@@ -136,6 +158,20 @@ 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

@@ -135,6 +135,31 @@ 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

@@ -19,6 +19,7 @@
 #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>
@@ -332,6 +333,7 @@ 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)
@@ -377,6 +379,25 @@ 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

@@ -177,8 +177,11 @@ struct external_constructor<value_t::array>
     }
 
     template < typename BasicJsonType, typename CompatibleArrayType,
-               enable_if_t < !std::is_same<CompatibleArrayType, typename BasicJsonType::array_t>::value,
+               enable_if_t < !std::is_same<CompatibleArrayType, typename BasicJsonType::array_t>::value
-                             int > = 0 >
+#if JSON_HAS_RANGES && !defined(__MINGW32__)
+                             && !is_compatible_range_view<CompatibleArrayType>::value
+#endif
+                             , int > = 0 >
     static void construct(BasicJsonType& j, const CompatibleArrayType& arr)
     {
         using std::begin;
@@ -218,6 +221,25 @@ struct external_constructor<value_t::array>
         j.set_parents();
         j.assert_invariant();
     }
+
+    // std::ranges does not work properly on MinGW due to incomplete C++20 support
+    // see https://github.com/nlohmann/json/issues/4916
+#if JSON_HAS_RANGES && !defined(__MINGW32__)
+    template<typename BasicJsonType, typename CompatibleArrayType,
+             enable_if_t<is_compatible_range_view<std::remove_cvref_t<CompatibleArrayType>>::value, int> = 0>
+    static void construct(BasicJsonType& j, CompatibleArrayType && arr)
+    {
+        j.m_data.m_value.destroy(j.m_data.m_type);
+        j.m_data.m_type = value_t::array;
+        j.m_data.m_value = value_t::array;
+        for (auto&& x : std::forward<CompatibleArrayType>(arr))
+        {
+            j.m_data.m_value.array->push_back(x);
+            j.set_parent(j.m_data.m_value.array->back());
+        }
+        j.assert_invariant();
+    }
+#endif
 };
 
 template<>
@@ -355,19 +377,44 @@ 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_basic_json<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
+#endif
+                         ,
                          int > = 0 >
 inline void to_json(BasicJsonType& j, const CompatibleArrayType& arr)
 {
     external_constructor<value_t::array>::construct(j, arr);
 }
 
+#if JSON_HAS_RANGES && !defined(__MINGW32__)
+template < typename BasicJsonType, typename T,
+           enable_if_t < is_compatible_range_view<std::remove_cvref_t<T>>::value
+                         && !is_compatible_string_type<BasicJsonType, std::remove_cvref_t<T>>::value
+                         && !is_compatible_object_type<BasicJsonType, std::remove_cvref_t<T>>::value
+                         && !is_basic_json<std::remove_cvref_t<T>>::value, int > = 0 >
+inline void to_json(BasicJsonType& j, T && arr)
+{
+    external_constructor<value_t::array>::construct(j, std::forward<T>(arr));
+}
+#endif
+
 template<typename BasicJsonType>
 inline void to_json(BasicJsonType& j, const typename BasicJsonType::binary_t& bin)
 {
     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

@@ -155,7 +155,9 @@ 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.
-template<typename IteratorType>
+// 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>
 class iterator_input_adapter
 {
   public:
@@ -169,9 +171,10 @@ 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, IteratorType last)
+    iterator_input_adapter(IteratorType first, SentinelType last)
         : begin(first), current(std::move(first)), end(std::move(last))
     {}
 
@@ -216,19 +219,30 @@ 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)
+    // library iterators such as those of std::vector and std::string).
+    // Computing the available element count needs either same-type iterators
+    // (plain std::distance) or, in C++20, a sized sentinel (std::ranges::distance),
+    // e.g. std::counted_iterator paired with std::default_sentinel_t.
     static constexpr bool iterator_is_contiguous =
 #if defined(__cpp_lib_concepts) && defined(JSON_HAS_CPP_20)
-        std::contiguous_iterator<IteratorType> ||
+        (std::is_same<IteratorType, SentinelType>::value || std::sized_sentinel_for<SentinelType, IteratorType>)
+        && (std::contiguous_iterator<IteratorType> || std::is_pointer<IteratorType>::value);
+#else
+        std::is_same<IteratorType, SentinelType>::value && std::is_pointer<IteratorType>::value;
 #endif
-        std::is_pointer<IteratorType>::value;
 
     // contiguous fast path: bulk copy the remaining range with std::memcpy
     template<class T>
     std::size_t get_elements_impl(T* dest, std::size_t count, std::true_type /*contiguous*/)
     {
         const std::size_t wanted = count * sizeof(T);
+#if defined(__cpp_lib_concepts) && defined(JSON_HAS_CPP_20)
+        // std::ranges::distance also supports sized sentinels of a different
+        // type (e.g. std::counted_iterator + std::default_sentinel_t)
+        const std::size_t available = static_cast<std::size_t>(std::ranges::distance(current, end)) * sizeof(char_type);
+#else
         const std::size_t available = static_cast<std::size_t>(std::distance(current, end)) * sizeof(char_type);
+#endif
         const std::size_t copied = (std::min)(wanted, available);
         if (JSON_HEDLEY_LIKELY(copied != 0))
         {
@@ -267,7 +281,7 @@ class iterator_input_adapter
 
     IteratorType begin;
     IteratorType current;
-    IteratorType end;
+    SentinelType end;
 
     template<typename BaseInputAdapter, size_t T>
     friend struct wide_string_input_helper;
@@ -453,19 +467,54 @@ class wide_string_input_adapter
     std::size_t utf8_bytes_filled = 0;
 };
 
-template<typename IteratorType, typename Enable = void>
+template<typename IteratorType, typename SentinelType = 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>;
+    using adapter_type = iterator_input_adapter<iterator_type, sentinel_type>;
 
-    static adapter_type create(IteratorType first, IteratorType last)
+    static adapter_type create(IteratorType first, SentinelType 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
 {
@@ -476,25 +525,31 @@ struct is_iterator_of_multibyte
     };
 };
 
-template<typename IteratorType>
+template<typename IteratorType, typename SentinelType>
-struct iterator_input_adapter_factory<IteratorType, enable_if_t<is_iterator_of_multibyte<IteratorType>::value>>
+struct iterator_input_adapter_factory<IteratorType, SentinelType, 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>;
+    using base_adapter_type = iterator_input_adapter<iterator_type, sentinel_type>;
     using adapter_type = wide_string_input_adapter<base_adapter_type, char_type>;
 
-    static adapter_type create(IteratorType first, IteratorType last)
+    static adapter_type create(IteratorType first, SentinelType last)
     {
         return adapter_type(base_adapter_type(std::move(first), std::move(last)));
     }
 };
 
-// General purpose iterator-based input
+// General purpose iterator-based input (iterator+sentinel pair; SentinelType
-template<typename IteratorType>
+// defaults to IteratorType for the common same-type case, but may differ for
-typename iterator_input_adapter_factory<IteratorType>::adapter_type input_adapter(IteratorType first, IteratorType last)
+// 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)
 {
-    using factory_type = iterator_input_adapter_factory<IteratorType>;
+    using factory_type = iterator_input_adapter_factory<IteratorType, SentinelType>;
     return factory_type::create(first, last);
 }
 

include/nlohmann/detail/meta/type_traits.hpp

@@ -13,11 +13,15 @@
 #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
 #include <nlohmann/detail/iterators/iterator_traits.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
+#ifdef JSON_HAS_CPP_17
+    #include <optional> // optional
+#endif
 #include <nlohmann/detail/meta/call_std/begin.hpp>
 #include <nlohmann/detail/meta/call_std/end.hpp>
 #include <nlohmann/detail/meta/cpp_future.hpp>
@@ -450,6 +454,51 @@ struct is_constructible_string_type
         value_type_t, laundered_type >>::value;
 };
 
+// Forward declarations: iteration_proxy.hpp includes this file, so we cannot
+// include it here.
+template<typename IteratorType> class iteration_proxy;
+template<typename IteratorType> class iteration_proxy_value;
+
+// Identifies nlohmann's internal iteration-proxy types. These must be excluded
+// before evaluating any std::ranges concept to avoid circular constraints.
+template<typename T> struct is_iteration_proxy_type : std::false_type {};
+template<typename T> struct is_iteration_proxy_type<iteration_proxy<T>>       : std::true_type {};
+template<typename T> struct is_iteration_proxy_type<iteration_proxy_value<T>> : std::true_type {};
+
+// In C++26, std::optional satisfies std::ranges::view; exclude it so the
+// range-view overload does not hijack the optional serializer.
+#ifdef JSON_HAS_CPP_17
+template<typename T> struct is_range_view_optional_type : std::false_type {};
+template<typename T> struct is_range_view_optional_type<std::optional<T>> : std::true_type {};
+#else
+template<typename T> struct is_range_view_optional_type : std::false_type {};
+#endif
+
+// std::ranges does not work properly on MinGW due to incomplete C++20 support
+// see https://github.com/nlohmann/json/issues/4916
+#if JSON_HAS_RANGES && !defined(__MINGW32__)
+
+// SafeToCheck guards against types that trigger circular constraints when
+// std::ranges::view<T> is evaluated on GCC 12 / libstdc++ 12:
+//   - iteration_proxy / iteration_proxy_value directly
+//   - views wrapping the above (e.g. owning_view<iteration_proxy<...>>)
+//   - views wrapping basic_json (e.g. ref_view<json>) — same circularity
+//     via json's constructors → is_compatible_array_type → here
+// nlohmann's plain range_value_t (iterator_traits-based) is safe to call
+// before any std::ranges concept is touched, so we use it for the checks.
+template < typename T, bool SafeToCheck =
+           !is_iteration_proxy_type<T>::value &&
+           !is_iteration_proxy_type<detected_t<range_value_t, T>>::value &&
+           !is_basic_json<detected_t<range_value_t, T>>::value &&
+           !is_range_view_optional_type<T>::value >
+struct is_compatible_range_view : std::false_type {};
+
+template<typename T>
+struct is_compatible_range_view<T, true>
+    : std::bool_constant<std::ranges::view<T>> {};
+
+#endif
+
 template<typename BasicJsonType, typename CompatibleArrayType, typename = void>
 struct is_compatible_array_type_impl : std::false_type {};
 
@@ -461,13 +510,38 @@ struct is_compatible_array_type_impl <
     is_iterator_traits<iterator_traits<detected_t<iterator_t, CompatibleArrayType>>>::value&&
 // special case for types like std::filesystem::path whose iterator's value_type are themselves
 // c.f. https://github.com/nlohmann/json/pull/3073
-    !std::is_same<CompatibleArrayType, detected_t<range_value_t, CompatibleArrayType>>::value >>
+    !std::is_same<CompatibleArrayType, detected_t<range_value_t, CompatibleArrayType>>::value
+// When range-view support is enabled, std::ranges::view types (e.g. std::string_view,
+// filter_view) can match BOTH this iterator-based specialization AND the view-based one
+// below, causing ambiguity. Exclude views here so the two specializations are mutually
+// exclusive: this one handles plain iterable containers, the other handles views.
+#if JSON_HAS_RANGES && !defined(__MINGW32__)
+&& !is_compatible_range_view<CompatibleArrayType>::value
+#endif
+            >>
 {
     static constexpr bool value =
         is_constructible<BasicJsonType,
         range_value_t<CompatibleArrayType>>::value;
 };
 
+#if JSON_HAS_RANGES && !defined(__MINGW32__)
+template<typename BasicJsonType, typename CompatibleArrayType>
+struct is_compatible_array_type_impl <
+    BasicJsonType, CompatibleArrayType,
+    enable_if_t < is_compatible_range_view<CompatibleArrayType>::value
+    && !std::is_same<detected_t<range_value_t, CompatibleArrayType>, char>::value
+    && !std::is_same<detected_t<range_value_t, CompatibleArrayType>, wchar_t>::value >>
+{
+    // CompatibleArrayType is a std::ranges::view here, so std::ranges::range_value_t
+    // is safe and correctly handles C++20 iterators that may lack classic iterator_traits.
+    static constexpr bool value =
+        is_constructible<BasicJsonType,
+        std::ranges::range_value_t<CompatibleArrayType>>::value;
+};
+#endif
+
+
 template<typename BasicJsonType, typename CompatibleArrayType>
 struct is_compatible_array_type
     : is_compatible_array_type_impl<BasicJsonType, CompatibleArrayType> {};
@@ -559,6 +633,14 @@ 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

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

single_include/nlohmann/json.hpp

@@ -189,6 +189,7 @@
 #include <unordered_map> // unordered_map
 #include <utility> // pair, declval
 #include <valarray> // valarray
+#include <vector> // vector
 
 // #include <nlohmann/detail/exceptions.hpp>
 //     __ _____ _____ _____
@@ -3592,6 +3593,7 @@ 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
@@ -3663,6 +3665,9 @@ NLOHMANN_JSON_NAMESPACE_END
 
 // #include <nlohmann/detail/macro_scope.hpp>
 
+#ifdef JSON_HAS_CPP_17
+    #include <optional> // optional
+#endif
 // #include <nlohmann/detail/meta/call_std/begin.hpp>
 //     __ _____ _____ _____
 //  __|  |   __|     |   | |  JSON for Modern C++
@@ -4212,6 +4217,51 @@ struct is_constructible_string_type
         value_type_t, laundered_type >>::value;
 };
 
+// Forward declarations: iteration_proxy.hpp includes this file, so we cannot
+// include it here.
+template<typename IteratorType> class iteration_proxy;
+template<typename IteratorType> class iteration_proxy_value;
+
+// Identifies nlohmann's internal iteration-proxy types. These must be excluded
+// before evaluating any std::ranges concept to avoid circular constraints.
+template<typename T> struct is_iteration_proxy_type : std::false_type {};
+template<typename T> struct is_iteration_proxy_type<iteration_proxy<T>>       : std::true_type {};
+template<typename T> struct is_iteration_proxy_type<iteration_proxy_value<T>> : std::true_type {};
+
+// In C++26, std::optional satisfies std::ranges::view; exclude it so the
+// range-view overload does not hijack the optional serializer.
+#ifdef JSON_HAS_CPP_17
+template<typename T> struct is_range_view_optional_type : std::false_type {};
+template<typename T> struct is_range_view_optional_type<std::optional<T>> : std::true_type {};
+#else
+template<typename T> struct is_range_view_optional_type : std::false_type {};
+#endif
+
+// std::ranges does not work properly on MinGW due to incomplete C++20 support
+// see https://github.com/nlohmann/json/issues/4916
+#if JSON_HAS_RANGES && !defined(__MINGW32__)
+
+// SafeToCheck guards against types that trigger circular constraints when
+// std::ranges::view<T> is evaluated on GCC 12 / libstdc++ 12:
+//   - iteration_proxy / iteration_proxy_value directly
+//   - views wrapping the above (e.g. owning_view<iteration_proxy<...>>)
+//   - views wrapping basic_json (e.g. ref_view<json>) — same circularity
+//     via json's constructors → is_compatible_array_type → here
+// nlohmann's plain range_value_t (iterator_traits-based) is safe to call
+// before any std::ranges concept is touched, so we use it for the checks.
+template < typename T, bool SafeToCheck =
+           !is_iteration_proxy_type<T>::value &&
+           !is_iteration_proxy_type<detected_t<range_value_t, T>>::value &&
+           !is_basic_json<detected_t<range_value_t, T>>::value &&
+           !is_range_view_optional_type<T>::value >
+struct is_compatible_range_view : std::false_type {};
+
+template<typename T>
+struct is_compatible_range_view<T, true>
+    : std::bool_constant<std::ranges::view<T>> {};
+
+#endif
+
 template<typename BasicJsonType, typename CompatibleArrayType, typename = void>
 struct is_compatible_array_type_impl : std::false_type {};
 
@@ -4223,13 +4273,38 @@ struct is_compatible_array_type_impl <
     is_iterator_traits<iterator_traits<detected_t<iterator_t, CompatibleArrayType>>>::value&&
 // special case for types like std::filesystem::path whose iterator's value_type are themselves
 // c.f. https://github.com/nlohmann/json/pull/3073
-    !std::is_same<CompatibleArrayType, detected_t<range_value_t, CompatibleArrayType>>::value >>
+    !std::is_same<CompatibleArrayType, detected_t<range_value_t, CompatibleArrayType>>::value
+// When range-view support is enabled, std::ranges::view types (e.g. std::string_view,
+// filter_view) can match BOTH this iterator-based specialization AND the view-based one
+// below, causing ambiguity. Exclude views here so the two specializations are mutually
+// exclusive: this one handles plain iterable containers, the other handles views.
+#if JSON_HAS_RANGES && !defined(__MINGW32__)
+&& !is_compatible_range_view<CompatibleArrayType>::value
+#endif
+            >>
 {
     static constexpr bool value =
         is_constructible<BasicJsonType,
         range_value_t<CompatibleArrayType>>::value;
 };
 
+#if JSON_HAS_RANGES && !defined(__MINGW32__)
+template<typename BasicJsonType, typename CompatibleArrayType>
+struct is_compatible_array_type_impl <
+    BasicJsonType, CompatibleArrayType,
+    enable_if_t < is_compatible_range_view<CompatibleArrayType>::value
+    && !std::is_same<detected_t<range_value_t, CompatibleArrayType>, char>::value
+    && !std::is_same<detected_t<range_value_t, CompatibleArrayType>, wchar_t>::value >>
+{
+    // CompatibleArrayType is a std::ranges::view here, so std::ranges::range_value_t
+    // is safe and correctly handles C++20 iterators that may lack classic iterator_traits.
+    static constexpr bool value =
+        is_constructible<BasicJsonType,
+        std::ranges::range_value_t<CompatibleArrayType>>::value;
+};
+#endif
+
+
 template<typename BasicJsonType, typename CompatibleArrayType>
 struct is_compatible_array_type
     : is_compatible_array_type_impl<BasicJsonType, CompatibleArrayType> {};
@@ -4321,6 +4396,14 @@ 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
 {
@@ -5464,6 +5547,7 @@ 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)
@@ -5509,6 +5593,25 @@ 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)
@@ -6205,8 +6308,11 @@ struct external_constructor<value_t::array>
     }
 
     template < typename BasicJsonType, typename CompatibleArrayType,
-               enable_if_t < !std::is_same<CompatibleArrayType, typename BasicJsonType::array_t>::value,
+               enable_if_t < !std::is_same<CompatibleArrayType, typename BasicJsonType::array_t>::value
-                             int > = 0 >
+#if JSON_HAS_RANGES && !defined(__MINGW32__)
+                             && !is_compatible_range_view<CompatibleArrayType>::value
+#endif
+                             , int > = 0 >
     static void construct(BasicJsonType& j, const CompatibleArrayType& arr)
     {
         using std::begin;
@@ -6246,6 +6352,25 @@ struct external_constructor<value_t::array>
         j.set_parents();
         j.assert_invariant();
     }
+
+    // std::ranges does not work properly on MinGW due to incomplete C++20 support
+    // see https://github.com/nlohmann/json/issues/4916
+#if JSON_HAS_RANGES && !defined(__MINGW32__)
+    template<typename BasicJsonType, typename CompatibleArrayType,
+             enable_if_t<is_compatible_range_view<std::remove_cvref_t<CompatibleArrayType>>::value, int> = 0>
+    static void construct(BasicJsonType& j, CompatibleArrayType && arr)
+    {
+        j.m_data.m_value.destroy(j.m_data.m_type);
+        j.m_data.m_type = value_t::array;
+        j.m_data.m_value = value_t::array;
+        for (auto&& x : std::forward<CompatibleArrayType>(arr))
+        {
+            j.m_data.m_value.array->push_back(x);
+            j.set_parent(j.m_data.m_value.array->back());
+        }
+        j.assert_invariant();
+    }
+#endif
 };
 
 template<>
@@ -6383,19 +6508,44 @@ 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_basic_json<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
+#endif
+                         ,
                          int > = 0 >
 inline void to_json(BasicJsonType& j, const CompatibleArrayType& arr)
 {
     external_constructor<value_t::array>::construct(j, arr);
 }
 
+#if JSON_HAS_RANGES && !defined(__MINGW32__)
+template < typename BasicJsonType, typename T,
+           enable_if_t < is_compatible_range_view<std::remove_cvref_t<T>>::value
+                         && !is_compatible_string_type<BasicJsonType, std::remove_cvref_t<T>>::value
+                         && !is_compatible_object_type<BasicJsonType, std::remove_cvref_t<T>>::value
+                         && !is_basic_json<std::remove_cvref_t<T>>::value, int > = 0 >
+inline void to_json(BasicJsonType& j, T && arr)
+{
+    external_constructor<value_t::array>::construct(j, std::forward<T>(arr));
+}
+#endif
+
 template<typename BasicJsonType>
 inline void to_json(BasicJsonType& j, const typename BasicJsonType::binary_t& bin)
 {
     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)
@@ -6992,7 +7142,9 @@ 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.
-template<typename IteratorType>
+// 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>
 class iterator_input_adapter
 {
   public:
@@ -7006,9 +7158,10 @@ 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, IteratorType last)
+    iterator_input_adapter(IteratorType first, SentinelType last)
         : begin(first), current(std::move(first)), end(std::move(last))
     {}
 
@@ -7053,19 +7206,30 @@ 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)
+    // library iterators such as those of std::vector and std::string).
+    // Computing the available element count needs either same-type iterators
+    // (plain std::distance) or, in C++20, a sized sentinel (std::ranges::distance),
+    // e.g. std::counted_iterator paired with std::default_sentinel_t.
     static constexpr bool iterator_is_contiguous =
 #if defined(__cpp_lib_concepts) && defined(JSON_HAS_CPP_20)
-        std::contiguous_iterator<IteratorType> ||
+        (std::is_same<IteratorType, SentinelType>::value || std::sized_sentinel_for<SentinelType, IteratorType>)
+        && (std::contiguous_iterator<IteratorType> || std::is_pointer<IteratorType>::value);
+#else
+        std::is_same<IteratorType, SentinelType>::value && std::is_pointer<IteratorType>::value;
 #endif
-        std::is_pointer<IteratorType>::value;
 
     // contiguous fast path: bulk copy the remaining range with std::memcpy
     template<class T>
     std::size_t get_elements_impl(T* dest, std::size_t count, std::true_type /*contiguous*/)
     {
         const std::size_t wanted = count * sizeof(T);
+#if defined(__cpp_lib_concepts) && defined(JSON_HAS_CPP_20)
+        // std::ranges::distance also supports sized sentinels of a different
+        // type (e.g. std::counted_iterator + std::default_sentinel_t)
+        const std::size_t available = static_cast<std::size_t>(std::ranges::distance(current, end)) * sizeof(char_type);
+#else
         const std::size_t available = static_cast<std::size_t>(std::distance(current, end)) * sizeof(char_type);
+#endif
         const std::size_t copied = (std::min)(wanted, available);
         if (JSON_HEDLEY_LIKELY(copied != 0))
         {
@@ -7104,7 +7268,7 @@ class iterator_input_adapter
 
     IteratorType begin;
     IteratorType current;
-    IteratorType end;
+    SentinelType end;
 
     template<typename BaseInputAdapter, size_t T>
     friend struct wide_string_input_helper;
@@ -7290,19 +7454,54 @@ class wide_string_input_adapter
     std::size_t utf8_bytes_filled = 0;
 };
 
-template<typename IteratorType, typename Enable = void>
+template<typename IteratorType, typename SentinelType = 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>;
+    using adapter_type = iterator_input_adapter<iterator_type, sentinel_type>;
 
-    static adapter_type create(IteratorType first, IteratorType last)
+    static adapter_type create(IteratorType first, SentinelType 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
 {
@@ -7313,25 +7512,31 @@ struct is_iterator_of_multibyte
     };
 };
 
-template<typename IteratorType>
+template<typename IteratorType, typename SentinelType>
-struct iterator_input_adapter_factory<IteratorType, enable_if_t<is_iterator_of_multibyte<IteratorType>::value>>
+struct iterator_input_adapter_factory<IteratorType, SentinelType, 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>;
+    using base_adapter_type = iterator_input_adapter<iterator_type, sentinel_type>;
     using adapter_type = wide_string_input_adapter<base_adapter_type, char_type>;
 
-    static adapter_type create(IteratorType first, IteratorType last)
+    static adapter_type create(IteratorType first, SentinelType last)
     {
         return adapter_type(base_adapter_type(std::move(first), std::move(last)));
     }
 };
 
-// General purpose iterator-based input
+// General purpose iterator-based input (iterator+sentinel pair; SentinelType
-template<typename IteratorType>
+// defaults to IteratorType for the common same-type case, but may differ for
-typename iterator_input_adapter_factory<IteratorType>::adapter_type input_adapter(IteratorType first, IteratorType last)
+// 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)
 {
-    using factory_type = iterator_input_adapter_factory<IteratorType>;
+    using factory_type = iterator_input_adapter_factory<IteratorType, SentinelType>;
     return factory_type::create(first, last);
 }
 
@@ -24934,12 +25139,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return result;
     }
 
-    /// @brief deserialize from a pair of character iterators
+    /// @brief deserialize from a pair of character iterators (or an iterator+sentinel pair, C++20 ranges support)
     /// @sa https://json.nlohmann.me/api/basic_json/parse/
-    template<typename IteratorType>
+    template<typename IteratorType, typename SentinelType = IteratorType,
+             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json parse(IteratorType first,
-                            IteratorType last,
+                            SentinelType last,
                             parser_callback_t cb = nullptr,
                             const bool allow_exceptions = true,
                             const bool ignore_comments = false,
@@ -24973,10 +25179,11 @@ 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
+    /// @brief check if the input is valid JSON (iterator pair, or iterator+sentinel pair for C++20 ranges support)
     /// @sa https://json.nlohmann.me/api/basic_json/accept/
-    template<typename IteratorType>
+    template<typename IteratorType, typename SentinelType = IteratorType,
-    static bool accept(IteratorType first, IteratorType last,
+             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
+    static bool accept(IteratorType first, SentinelType last,
                        const bool ignore_comments = false,
                        const bool ignore_trailing_commas = false)
     {
@@ -25008,11 +25215,12 @@ 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
+    /// @brief generate SAX events (iterator pair, or iterator+sentinel pair for C++20 ranges support)
     /// @sa https://json.nlohmann.me/api/basic_json/sax_parse/
-    template<class IteratorType, class SAX>
+    template<class IteratorType, class SAX, class SentinelType = IteratorType,
+             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
     JSON_HEDLEY_NON_NULL(3)
-    static bool sax_parse(IteratorType first, IteratorType last, SAX* sax,
+    static bool sax_parse(IteratorType first, SentinelType last, SAX* sax,
                           input_format_t format = input_format_t::json,
                           const bool strict = true,
                           const bool ignore_comments = false,
@@ -25312,11 +25520,12 @@ 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
+    /// @brief create a JSON value from an input in CBOR format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
     /// @sa https://json.nlohmann.me/api/basic_json/from_cbor/
-    template<typename IteratorType>
+    template<typename IteratorType, typename SentinelType = IteratorType,
+             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
     JSON_HEDLEY_WARN_UNUSED_RESULT
-    static basic_json from_cbor(IteratorType first, IteratorType last,
+    static basic_json from_cbor(IteratorType first, SentinelType last,
                                 const bool strict = true,
                                 const bool allow_exceptions = true,
                                 const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error)
@@ -25369,11 +25578,12 @@ 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
+    /// @brief create a JSON value from an input in MessagePack format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
     /// @sa https://json.nlohmann.me/api/basic_json/from_msgpack/
-    template<typename IteratorType>
+    template<typename IteratorType, typename SentinelType = IteratorType,
+             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
     JSON_HEDLEY_WARN_UNUSED_RESULT
-    static basic_json from_msgpack(IteratorType first, IteratorType last,
+    static basic_json from_msgpack(IteratorType first, SentinelType last,
                                    const bool strict = true,
                                    const bool allow_exceptions = true)
     {
@@ -25423,11 +25633,12 @@ 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
+    /// @brief create a JSON value from an input in UBJSON format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
     /// @sa https://json.nlohmann.me/api/basic_json/from_ubjson/
-    template<typename IteratorType>
+    template<typename IteratorType, typename SentinelType = IteratorType,
+             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
     JSON_HEDLEY_WARN_UNUSED_RESULT
-    static basic_json from_ubjson(IteratorType first, IteratorType last,
+    static basic_json from_ubjson(IteratorType first, SentinelType last,
                                   const bool strict = true,
                                   const bool allow_exceptions = true)
     {
@@ -25477,11 +25688,12 @@ 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
+    /// @brief create a JSON value from an input in BJData format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
     /// @sa https://json.nlohmann.me/api/basic_json/from_bjdata/
-    template<typename IteratorType>
+    template<typename IteratorType, typename SentinelType = IteratorType,
+             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
     JSON_HEDLEY_WARN_UNUSED_RESULT
-    static basic_json from_bjdata(IteratorType first, IteratorType last,
+    static basic_json from_bjdata(IteratorType first, SentinelType last,
                                   const bool strict = true,
                                   const bool allow_exceptions = true)
     {
@@ -25507,11 +25719,12 @@ 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
+    /// @brief create a JSON value from an input in BSON format (iterator pair, or iterator+sentinel pair for C++20 ranges support)
     /// @sa https://json.nlohmann.me/api/basic_json/from_bson/
-    template<typename IteratorType>
+    template<typename IteratorType, typename SentinelType = IteratorType,
+             detail::enable_if_t<detail::can_compare_ne<IteratorType, SentinelType>::value, int> = 0>
     JSON_HEDLEY_WARN_UNUSED_RESULT
-    static basic_json from_bson(IteratorType first, IteratorType last,
+    static basic_json from_bson(IteratorType first, SentinelType last,
                                 const bool strict = true,
                                 const bool allow_exceptions = true)
     {

tests/src/test_utils.hpp

@@ -30,4 +30,17 @@ 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

@@ -3699,6 +3699,15 @@ 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

@@ -1208,6 +1208,19 @@ 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

@@ -1921,6 +1921,15 @@ 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

@@ -1641,6 +1641,15 @@ 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

@@ -1136,6 +1136,40 @@ 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{};
@@ -1165,6 +1199,46 @@ TEST_CASE("regression tests 2")
     }
 #endif
 
+#if JSON_HAS_RANGES && !defined(__MINGW32__)
+    SECTION("issue #4916 - constructing array from C++20 ranges view does not work")
+    {
+        std::vector<int> nums{1, 2, 37, 42, 21};
+        auto filteredNums = nums | std::views::filter([](int i)
+        {
+            return i > 10;
+        });
+        json const j(filteredNums);
+        CHECK(j.type() == json::value_t::array);
+        CHECK(j == json({37, 42, 21}));
+    }
+#endif
+
+    // owning_view is not available in libstdc++ < 12
+#if JSON_HAS_RANGES && !defined(__MINGW32__) && !(defined(__GLIBCXX__) && _GLIBCXX_RELEASE < 12)
+    SECTION("issue #4916 - constructing array from prvalue C++20 ranges view (owning_view)")
+    {
+        json const j(std::vector<int> {1, 2, 37, 42, 21} | std::views::filter([](int i)
+        {
+            return i > 10;
+        }));
+        CHECK(j.type() == json::value_t::array);
+        CHECK(j == json({37, 42, 21}));
+    }
+#endif
+
+#if JSON_HAS_RANGES && !defined(__MINGW32__)
+    SECTION("issue #4916 - constructing array from C++20 transform view (prvalue elements)")
+    {
+        std::vector<int> nums{1, 2, 3};
+        auto t = nums | std::views::transform([](int i) noexcept
+        {
+            return i * 2;
+        });
+        json const j(t);
+        CHECK(j.type() == json::value_t::array);
+        CHECK(j == json({2, 4, 6}));
+    }
+#endif
 }
 
 TEST_CASE_TEMPLATE("issue #4798 - nlohmann::json::to_msgpack() encode float NaN as double", T, double, float) // NOLINT(readability-math-missing-parentheses, bugprone-throwing-static-initialization)

tests/src/unit-ubjson.cpp

@@ -2393,6 +2393,15 @@ 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

@@ -6,6 +6,13 @@
 // SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
 // SPDX-License-Identifier: MIT
 
+// cmake/test.cmake selects the C++ standard versions with which to build a
+// unit test based on the presence of JSON_HAS_CPP_<VERSION> macros.
+// When using macros that are only defined for particular versions of the standard
+// (e.g., JSON_HAS_FILESYSTEM for C++17 and up), please mention the corresponding
+// version macro in a comment close by, like this:
+// JSON_HAS_CPP_<VERSION> (do not remove; see note at top of file)
+
 #include "doctest_compatibility.h"
 
 #include <nlohmann/json.hpp>
@@ -13,6 +20,10 @@ using nlohmann::json;
 
 #include <list>
 
+#if defined(__cpp_lib_concepts) && defined(JSON_HAS_CPP_20)
+    #include <iterator>
+#endif
+
 namespace
 {
 TEST_CASE("Use arbitrary stdlib container")
@@ -168,4 +179,55 @@ 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);
+}
+
+#if defined(__cpp_lib_concepts) && defined(JSON_HAS_CPP_20)
+// JSON_HAS_CPP_20 (do not remove; see note at top of file)
+TEST_CASE("Parse with std::counted_iterator and std::default_sentinel_t")
+{
+    using iterator_type = std::string::const_iterator;
+    const std::string json_str = R"({"key":"value","array":[1,2,3]})";
+    const auto len = static_cast<std::iter_difference_t<iterator_type>>(json_str.size());
+
+    const std::counted_iterator<iterator_type> first(json_str.begin(), len);
+    const json j = json::parse(first, std::default_sentinel);
+    CHECK(j["key"] == "value");
+    CHECK(j["array"].size() == 3);
+
+    const std::counted_iterator<iterator_type> first2(json_str.begin(), len);
+    CHECK(json::accept(first2, std::default_sentinel));
+}
+#endif
+
 } // namespace