Add with_*_t alias templates to create basic_json types with changed template parameters (#5758)

* Add helper types to make it easier to create a basic_json type with modified template parameters

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

* Rename with_changed_*_t aliases to with_*_t and merge integer/unsigned aliases

Per review discussion on #3898 between gregmarr and nlohmann:
- rename with_changed_X_t to with_X_t for brevity
- replace the separate with_changed_integer_t/with_changed_unsigned_t
  aliases with a single with_integers_t<NumberIntegerType2, NumberUnsignedType2>
- add @sa doc comment links for the upcoming documentation page

Co-authored-by: Raphael Grimm <1005058+barcode@users.noreply.github.com>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Add documentation for the with_*_t member alias templates

Add docs/mkdocs/docs/api/basic_json/with_t.md documenting with_object_t,
with_array_t, with_string_t, with_boolean_t, with_integers_t, with_float_t,
with_allocator_t, with_json_serializer_t, with_binary_t and with_base_class_t,
with an accompanying example, and link the page from the basic_json member
types list and the mkdocs navigation.

Co-authored-by: Raphael Grimm <1005058+barcode@users.noreply.github.com>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Add tests for the with_*_t member alias templates

Check with std::is_same that each with_*_t alias produces the expected
basic_json type, and that with_string_t keeps nlohmann::ordered_map as
the object type when used on ordered_json.

Co-authored-by: Raphael Grimm <1005058+barcode@users.noreply.github.com>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Fix with_t nav entry and document chaining of the with_*_t aliases

Indent the with_t entry in mkdocs.yml so it is listed under basic_json,
explain that the aliases can be chained and work on ordered_json, and
test both, including json::with_object_t<ordered_map> == ordered_json.

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

* Add docset entry for basic_json::with_t

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: barcode <barcode@example.com>
Co-authored-by: Raphael Grimm <1005058+barcode@users.noreply.github.com>

include/nlohmann/json.hpp

@@ -226,6 +226,70 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// SAX interface type, see @ref nlohmann::json_sax
     using json_sax_t = json_sax<basic_json>;
 
+    ////////////////////////////////////////////////////////////////////////////////
+    // utility templates to create a json type with different template parameters //
+    ////////////////////////////////////////////////////////////////////////////////
+
+    /// Json type using a different type for storing objects
+    /// @sa https://json.nlohmann.me/api/basic_json/with_t/
+    template<template<typename, typename, typename...> class ObjectType2>
+    using with_object_t = basic_json<ObjectType2, ArrayType, StringType, BooleanType,
+          NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
+
+    /// Json type using a different type for storing arrays
+    /// @sa https://json.nlohmann.me/api/basic_json/with_t/
+    template<template<typename, typename...> class ArrayType2>
+    using with_array_t =  basic_json<ObjectType, ArrayType2, StringType, BooleanType,
+          NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
+
+    /// Json type using a different type for storing strings
+    /// @sa https://json.nlohmann.me/api/basic_json/with_t/
+    template<class StringType2>
+    using with_string_t =  basic_json<ObjectType, ArrayType, StringType2, BooleanType,
+          NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
+
+    /// Json type using a different type for storing booleans
+    /// @sa https://json.nlohmann.me/api/basic_json/with_t/
+    template<class BooleanType2>
+    using with_boolean_t =  basic_json<ObjectType, ArrayType, StringType, BooleanType2,
+          NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
+
+    /// Json type using different types for storing signed and unsigned integers
+    /// @sa https://json.nlohmann.me/api/basic_json/with_t/
+    template<class NumberIntegerType2, class NumberUnsignedType2>
+    using with_integers_t =  basic_json<ObjectType, ArrayType, StringType, BooleanType,
+          NumberIntegerType2, NumberUnsignedType2, NumberFloatType, AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
+
+    /// Json type using a different type for storing floating point numbers
+    /// @sa https://json.nlohmann.me/api/basic_json/with_t/
+    template<class NumberFloatType2>
+    using with_float_t =  basic_json<ObjectType, ArrayType, StringType, BooleanType,
+          NumberIntegerType, NumberUnsignedType, NumberFloatType2, AllocatorType, JSONSerializer, BinaryType, CustomBaseClass>;
+
+    /// Json type using a different type as base allocator
+    /// @sa https://json.nlohmann.me/api/basic_json/with_t/
+    template<template<typename> class AllocatorType2>
+    using with_allocator_t =  basic_json<ObjectType, ArrayType, StringType, BooleanType,
+          NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType2, JSONSerializer, BinaryType, CustomBaseClass>;
+
+    /// Json type using a different type as json serializer
+    /// @sa https://json.nlohmann.me/api/basic_json/with_t/
+    template<template<typename, typename = void> class JSONSerializer2>
+    using with_json_serializer_t =  basic_json<ObjectType, ArrayType, StringType, BooleanType,
+          NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer2, BinaryType, CustomBaseClass>;
+
+    /// Json type using a different type for storing binary data
+    /// @sa https://json.nlohmann.me/api/basic_json/with_t/
+    template<class BinaryType2>
+    using with_binary_t =  basic_json<ObjectType, ArrayType, StringType, BooleanType,
+          NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType2, CustomBaseClass>;
+
+    /// Json type using a different type as base class
+    /// @sa https://json.nlohmann.me/api/basic_json/with_t/
+    template<class CustomBaseClass2>
+    using with_base_class_t =  basic_json<ObjectType, ArrayType, StringType, BooleanType,
+          NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType, CustomBaseClass2>;
+
     ////////////////
     // exceptions //
     ////////////////