🔀 merge develop

single_include/nlohmann/json.hpp

@@ -49,6 +49,7 @@ SOFTWARE.
 // #include <nlohmann/adl_serializer.hpp>
 
 
+#include <type_traits>
 #include <utility>
 
 // #include <nlohmann/detail/conversions/from_json.hpp>
@@ -2229,15 +2230,20 @@ JSON_HEDLEY_DIAGNOSTIC_POP
 #endif
 
 // C++ language standard detection
-#if (defined(__cplusplus) && __cplusplus >= 202002L) || (defined(_MSVC_LANG) && _MSVC_LANG >= 202002L)
-    #define JSON_HAS_CPP_20
-    #define JSON_HAS_CPP_17
-    #define JSON_HAS_CPP_14
-#elif (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_HAS_CXX17) && _HAS_CXX17 == 1) // fix for issue #464
-    #define JSON_HAS_CPP_17
-    #define JSON_HAS_CPP_14
-#elif (defined(__cplusplus) && __cplusplus >= 201402L) || (defined(_HAS_CXX14) && _HAS_CXX14 == 1)
-    #define JSON_HAS_CPP_14
+// if the user manually specified the used c++ version this is skipped
+#if !defined(JSON_HAS_CPP_20) && !defined(JSON_HAS_CPP_17) && !defined(JSON_HAS_CPP_14) && !defined(JSON_HAS_CPP_11)
+    #if (defined(__cplusplus) && __cplusplus >= 202002L) || (defined(_MSVC_LANG) && _MSVC_LANG >= 202002L)
+        #define JSON_HAS_CPP_20
+        #define JSON_HAS_CPP_17
+        #define JSON_HAS_CPP_14
+    #elif (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_HAS_CXX17) && _HAS_CXX17 == 1) // fix for issue #464
+        #define JSON_HAS_CPP_17
+        #define JSON_HAS_CPP_14
+    #elif (defined(__cplusplus) && __cplusplus >= 201402L) || (defined(_HAS_CXX14) && _HAS_CXX14 == 1)
+        #define JSON_HAS_CPP_14
+    #endif
+    // the cpp 11 flag is always specified because it is the minimal required version
+    #define JSON_HAS_CPP_11
 #endif
 
 // disable documentation warnings on clang
@@ -3166,6 +3172,18 @@ constexpr T static_const<T>::value;
 }  // namespace detail
 }  // namespace nlohmann
 
+// #include <nlohmann/detail/meta/identity_tag.hpp>
+
+
+namespace nlohmann
+{
+namespace detail
+{
+// dispatching helper struct
+template <class T> struct identity_tag {};
+}  // namespace detail
+}  // namespace nlohmann
+
 // #include <nlohmann/detail/meta/type_traits.hpp>
 
 
@@ -3483,8 +3501,7 @@ struct is_getable
 };
 
 template<typename BasicJsonType, typename T>
-struct has_from_json < BasicJsonType, T,
-           enable_if_t < !is_basic_json<T>::value >>
+struct has_from_json < BasicJsonType, T, enable_if_t < !is_basic_json<T>::value >>
 {
     using serializer = typename BasicJsonType::template json_serializer<T, void>;
 
@@ -3528,6 +3545,52 @@ struct has_to_json < BasicJsonType, T, enable_if_t < !is_basic_json<T>::value >>
 // is_ functions //
 ///////////////////
 
+// https://en.cppreference.com/w/cpp/types/conjunction
+template<class...> struct conjunction : std::true_type { };
+template<class B1> struct conjunction<B1> : B1 { };
+template<class B1, class... Bn>
+struct conjunction<B1, Bn...>
+: std::conditional<bool(B1::value), conjunction<Bn...>, B1>::type {};
+
+// Reimplementation of is_constructible and is_default_constructible, due to them being broken for
+// std::pair and std::tuple until LWG 2367 fix (see https://cplusplus.github.io/LWG/lwg-defects.html#2367).
+// This causes compile errors in e.g. clang 3.5 or gcc 4.9.
+template <typename T>
+struct is_default_constructible : std::is_default_constructible<T> {};
+
+template <typename T1, typename T2>
+struct is_default_constructible<std::pair<T1, T2>>
+            : conjunction<is_default_constructible<T1>, is_default_constructible<T2>> {};
+
+template <typename T1, typename T2>
+struct is_default_constructible<const std::pair<T1, T2>>
+            : conjunction<is_default_constructible<T1>, is_default_constructible<T2>> {};
+
+template <typename... Ts>
+struct is_default_constructible<std::tuple<Ts...>>
+            : conjunction<is_default_constructible<Ts>...> {};
+
+template <typename... Ts>
+struct is_default_constructible<const std::tuple<Ts...>>
+            : conjunction<is_default_constructible<Ts>...> {};
+
+
+template <typename T, typename... Args>
+struct is_constructible : std::is_constructible<T, Args...> {};
+
+template <typename T1, typename T2>
+struct is_constructible<std::pair<T1, T2>> : is_default_constructible<std::pair<T1, T2>> {};
+
+template <typename T1, typename T2>
+struct is_constructible<const std::pair<T1, T2>> : is_default_constructible<const std::pair<T1, T2>> {};
+
+template <typename... Ts>
+struct is_constructible<std::tuple<Ts...>> : is_default_constructible<std::tuple<Ts...>> {};
+
+template <typename... Ts>
+struct is_constructible<const std::tuple<Ts...>> : is_default_constructible<const std::tuple<Ts...>> {};
+
+
 template<typename T, typename = void>
 struct is_iterator_traits : std::false_type {};
 
@@ -3570,9 +3633,9 @@ struct is_compatible_object_type_impl <
 
     // macOS's is_constructible does not play well with nonesuch...
     static constexpr bool value =
-        std::is_constructible<typename object_t::key_type,
+        is_constructible<typename object_t::key_type,
         typename CompatibleObjectType::key_type>::value &&
-        std::is_constructible<typename object_t::mapped_type,
+        is_constructible<typename object_t::mapped_type,
         typename CompatibleObjectType::mapped_type>::value;
 };
 
@@ -3593,10 +3656,10 @@ struct is_constructible_object_type_impl <
     using object_t = typename BasicJsonType::object_t;
 
     static constexpr bool value =
-        (std::is_default_constructible<ConstructibleObjectType>::value &&
+        (is_default_constructible<ConstructibleObjectType>::value &&
          (std::is_move_assignable<ConstructibleObjectType>::value ||
           std::is_copy_assignable<ConstructibleObjectType>::value) &&
-         (std::is_constructible<typename ConstructibleObjectType::key_type,
+         (is_constructible<typename ConstructibleObjectType::key_type,
           typename object_t::key_type>::value &&
           std::is_same <
           typename object_t::mapped_type,
@@ -3624,7 +3687,7 @@ struct is_compatible_string_type_impl <
     value_type_t, CompatibleStringType>::value >>
 {
     static constexpr auto value =
-        std::is_constructible<typename BasicJsonType::string_t, CompatibleStringType>::value;
+        is_constructible<typename BasicJsonType::string_t, CompatibleStringType>::value;
 };
 
 template<typename BasicJsonType, typename ConstructibleStringType>
@@ -3642,7 +3705,7 @@ struct is_constructible_string_type_impl <
     value_type_t, ConstructibleStringType>::value >>
 {
     static constexpr auto value =
-        std::is_constructible<ConstructibleStringType,
+        is_constructible<ConstructibleStringType,
         typename BasicJsonType::string_t>::value;
 };
 
@@ -3665,7 +3728,7 @@ struct is_compatible_array_type_impl <
     iterator_traits<CompatibleArrayType >>::value >>
 {
     static constexpr bool value =
-        std::is_constructible<BasicJsonType,
+        is_constructible<BasicJsonType,
         typename CompatibleArrayType::value_type>::value;
 };
 
@@ -3688,7 +3751,7 @@ struct is_constructible_array_type_impl <
     BasicJsonType, ConstructibleArrayType,
     enable_if_t < !std::is_same<ConstructibleArrayType,
     typename BasicJsonType::value_type>::value&&
-    std::is_default_constructible<ConstructibleArrayType>::value&&
+    is_default_constructible<ConstructibleArrayType>::value&&
 (std::is_move_assignable<ConstructibleArrayType>::value ||
  std::is_copy_assignable<ConstructibleArrayType>::value)&&
 is_detected<value_type_t, ConstructibleArrayType>::value&&
@@ -3732,7 +3795,7 @@ struct is_compatible_integer_type_impl <
     using CompatibleLimits = std::numeric_limits<CompatibleNumberIntegerType>;
 
     static constexpr auto value =
-        std::is_constructible<RealIntegerType,
+        is_constructible<RealIntegerType,
         CompatibleNumberIntegerType>::value &&
         CompatibleLimits::is_integer &&
         RealLimits::is_signed == CompatibleLimits::is_signed;
@@ -3759,18 +3822,11 @@ template<typename BasicJsonType, typename CompatibleType>
 struct is_compatible_type
     : is_compatible_type_impl<BasicJsonType, CompatibleType> {};
 
-// https://en.cppreference.com/w/cpp/types/conjunction
-template<class...> struct conjunction : std::true_type { };
-template<class B1> struct conjunction<B1> : B1 { };
-template<class B1, class... Bn>
-struct conjunction<B1, Bn...>
-: std::conditional<bool(B1::value), conjunction<Bn...>, B1>::type {};
-
 template<typename T1, typename T2>
 struct is_constructible_tuple : std::false_type {};
 
 template<typename T1, typename... Args>
-struct is_constructible_tuple<T1, std::tuple<Args...>> : conjunction<std::is_constructible<T1, Args>...> {};
+struct is_constructible_tuple<T1, std::tuple<Args...>> : conjunction<is_constructible<T1, Args>...> {};
 
 /// type to check if KeyType can be used as object key
 template<typename BasicJsonType, typename KeyType>
@@ -3784,7 +3840,6 @@ struct is_key_type
                                   && !std::is_same<KeyType, typename BasicJsonType::iterator>::value
                                   && !std::is_same<KeyType, typename BasicJsonType::const_iterator>::value;
 };
-
 }  // namespace detail
 }  // namespace nlohmann
 
@@ -3960,7 +4015,10 @@ auto from_json_array_impl(const BasicJsonType& j, std::array<T, N>& arr,
     }
 }
 
-template<typename BasicJsonType, typename ConstructibleArrayType>
+template<typename BasicJsonType, typename ConstructibleArrayType,
+         enable_if_t<
+             std::is_assignable<ConstructibleArrayType&, ConstructibleArrayType>::value,
+             int> = 0>
 auto from_json_array_impl(const BasicJsonType& j, ConstructibleArrayType& arr, priority_tag<1> /*unused*/)
 -> decltype(
     arr.reserve(std::declval<typename ConstructibleArrayType::size_type>()),
@@ -3981,7 +4039,10 @@ auto from_json_array_impl(const BasicJsonType& j, ConstructibleArrayType& arr, p
     arr = std::move(ret);
 }
 
-template<typename BasicJsonType, typename ConstructibleArrayType>
+template<typename BasicJsonType, typename ConstructibleArrayType,
+         enable_if_t<
+             std::is_assignable<ConstructibleArrayType&, ConstructibleArrayType>::value,
+             int> = 0>
 void from_json_array_impl(const BasicJsonType& j, ConstructibleArrayType& arr,
                           priority_tag<0> /*unused*/)
 {
@@ -4020,6 +4081,25 @@ void())
     from_json_array_impl(j, arr, priority_tag<3> {});
 }
 
+template < typename BasicJsonType, typename T, std::size_t... Idx >
+std::array<T, sizeof...(Idx)> from_json_inplace_array_impl(BasicJsonType&& j,
+        identity_tag<std::array<T, sizeof...(Idx)>> /*unused*/, index_sequence<Idx...> /*unused*/)
+{
+    return { { std::forward<BasicJsonType>(j).at(Idx).template get<T>()... } };
+}
+
+template < typename BasicJsonType, typename T, std::size_t N >
+auto from_json(BasicJsonType&& j, identity_tag<std::array<T, N>> tag)
+-> decltype(from_json_inplace_array_impl(std::forward<BasicJsonType>(j), tag, make_index_sequence<N> {}))
+{
+    if (JSON_HEDLEY_UNLIKELY(!j.is_array()))
+    {
+        JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(j.type_name()), j));
+    }
+
+    return from_json_inplace_array_impl(std::forward<BasicJsonType>(j), tag, make_index_sequence<N> {});
+}
+
 template<typename BasicJsonType>
 void from_json(const BasicJsonType& j, typename BasicJsonType::binary_t& bin)
 {
@@ -4095,22 +4175,47 @@ void from_json(const BasicJsonType& j, ArithmeticType& val)
     }
 }
 
+template<typename BasicJsonType, typename... Args, std::size_t... Idx>
+std::tuple<Args...> from_json_tuple_impl_base(BasicJsonType&& j, index_sequence<Idx...> /*unused*/)
+{
+    return std::make_tuple(std::forward<BasicJsonType>(j).at(Idx).template get<Args>()...);
+}
+
+template < typename BasicJsonType, class A1, class A2 >
+std::pair<A1, A2> from_json_tuple_impl(BasicJsonType&& j, identity_tag<std::pair<A1, A2>> /*unused*/, priority_tag<0> /*unused*/)
+{
+    return {std::forward<BasicJsonType>(j).at(0).template get<A1>(),
+            std::forward<BasicJsonType>(j).at(1).template get<A2>()};
+}
+
 template<typename BasicJsonType, typename A1, typename A2>
-void from_json(const BasicJsonType& j, std::pair<A1, A2>& p)
+void from_json_tuple_impl(BasicJsonType&& j, std::pair<A1, A2>& p, priority_tag<1> /*unused*/)
 {
-    p = {j.at(0).template get<A1>(), j.at(1).template get<A2>()};
+    p = from_json_tuple_impl(std::forward<BasicJsonType>(j), identity_tag<std::pair<A1, A2>> {}, priority_tag<0> {});
 }
 
-template<typename BasicJsonType, typename Tuple, std::size_t... Idx>
-void from_json_tuple_impl(const BasicJsonType& j, Tuple& t, index_sequence<Idx...> /*unused*/)
+template<typename BasicJsonType, typename... Args>
+std::tuple<Args...> from_json_tuple_impl(BasicJsonType&& j, identity_tag<std::tuple<Args...>> /*unused*/, priority_tag<2> /*unused*/)
 {
-    t = std::make_tuple(j.at(Idx).template get<typename std::tuple_element<Idx, Tuple>::type>()...);
+    return from_json_tuple_impl_base<BasicJsonType, Args...>(std::forward<BasicJsonType>(j), index_sequence_for<Args...> {});
 }
 
 template<typename BasicJsonType, typename... Args>
-void from_json(const BasicJsonType& j, std::tuple<Args...>& t)
+void from_json_tuple_impl(BasicJsonType&& j, std::tuple<Args...>& t, priority_tag<3> /*unused*/)
 {
-    from_json_tuple_impl(j, t, index_sequence_for<Args...> {});
+    t = from_json_tuple_impl_base<BasicJsonType, Args...>(std::forward<BasicJsonType>(j), index_sequence_for<Args...> {});
+}
+
+template<typename BasicJsonType, typename TupleRelated>
+auto from_json(BasicJsonType&& j, TupleRelated&& t)
+-> decltype(from_json_tuple_impl(std::forward<BasicJsonType>(j), std::forward<TupleRelated>(t), priority_tag<3> {}))
+{
+    if (JSON_HEDLEY_UNLIKELY(!j.is_array()))
+    {
+        JSON_THROW(type_error::create(302, "type must be array, but is " + std::string(j.type_name()), j));
+    }
+
+    return from_json_tuple_impl(std::forward<BasicJsonType>(j), std::forward<TupleRelated>(t), priority_tag<3> {});
 }
 
 template < typename BasicJsonType, typename Key, typename Value, typename Compare, typename Allocator,
@@ -4156,11 +4261,11 @@ void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyE
 struct from_json_fn
 {
     template<typename BasicJsonType, typename T>
-    auto operator()(const BasicJsonType& j, T& val) const
-    noexcept(noexcept(from_json(j, val)))
-    -> decltype(from_json(j, val), void())
+    auto operator()(const BasicJsonType& j, T&& val) const
+    noexcept(noexcept(from_json(j, std::forward<T>(val))))
+    -> decltype(from_json(j, std::forward<T>(val)))
     {
-        return from_json(j, val);
+        return from_json(j, std::forward<T>(val));
     }
 };
 }  // namespace detail
@@ -4745,11 +4850,15 @@ constexpr const auto& to_json = detail::static_const<detail::to_json_fn>::value;
 } // namespace
 } // namespace nlohmann
 
+// #include <nlohmann/detail/meta/identity_tag.hpp>
+
+// #include <nlohmann/detail/meta/type_traits.hpp>
+
 
 namespace nlohmann
 {
 
-template<typename, typename>
+template<typename ValueType, typename>
 struct adl_serializer
 {
     /*!
@@ -4758,11 +4867,13 @@ struct adl_serializer
     This function is usually called by the `get()` function of the
     @ref basic_json class (either explicit or via conversion operators).
 
+    @note This function is chosen for default-constructible value types.
+
     @param[in] j        JSON value to read from
     @param[in,out] val  value to write to
     */
-    template<typename BasicJsonType, typename ValueType>
-    static auto from_json(BasicJsonType&& j, ValueType& val) noexcept(
+    template<typename BasicJsonType, typename TargetType = ValueType>
+    static auto from_json(BasicJsonType && j, TargetType& val) noexcept(
         noexcept(::nlohmann::from_json(std::forward<BasicJsonType>(j), val)))
     -> decltype(::nlohmann::from_json(std::forward<BasicJsonType>(j), val), void())
     {
@@ -4770,6 +4881,26 @@ struct adl_serializer
     }
 
     /*!
+    @brief convert a JSON value to any value type
+
+    This function is usually called by the `get()` function of the
+    @ref basic_json class (either explicit or via conversion operators).
+
+    @note This function is chosen for value types which are not default-constructible.
+
+    @param[in] j  JSON value to read from
+
+    @return copy of the JSON value, converted to @a ValueType
+    */
+    template<typename BasicJsonType, typename TargetType = ValueType>
+    static auto from_json(BasicJsonType && j) noexcept(
+    noexcept(::nlohmann::from_json(std::forward<BasicJsonType>(j), detail::identity_tag<TargetType> {})))
+    -> decltype(::nlohmann::from_json(std::forward<BasicJsonType>(j), detail::identity_tag<TargetType> {}))
+    {
+        return ::nlohmann::from_json(std::forward<BasicJsonType>(j), detail::identity_tag<TargetType> {});
+    }
+
+    /*!
     @brief convert any value type to a JSON value
 
     This function is usually called by the constructors of the @ref basic_json
@@ -4778,15 +4909,14 @@ struct adl_serializer
     @param[in,out] j  JSON value to write to
     @param[in] val    value to read from
     */
-    template<typename BasicJsonType, typename ValueType>
-    static auto to_json(BasicJsonType& j, ValueType&& val) noexcept(
-        noexcept(::nlohmann::to_json(j, std::forward<ValueType>(val))))
-    -> decltype(::nlohmann::to_json(j, std::forward<ValueType>(val)), void())
+    template<typename BasicJsonType, typename TargetType = ValueType>
+    static auto to_json(BasicJsonType& j, TargetType && val) noexcept(
+        noexcept(::nlohmann::to_json(j, std::forward<TargetType>(val))))
+    -> decltype(::nlohmann::to_json(j, std::forward<TargetType>(val)), void())
     {
-        ::nlohmann::to_json(j, std::forward<ValueType>(val));
+        ::nlohmann::to_json(j, std::forward<TargetType>(val));
     }
 };
-
 }  // namespace nlohmann
 
 // #include <nlohmann/byte_container_with_subtype.hpp>
@@ -6537,7 +6667,7 @@ class lexer : public lexer_base<BasicJsonType>
     /*!
     @brief scan a string literal
 
-    This function scans a string according to Sect. 7 of RFC 7159. While
+    This function scans a string according to Sect. 7 of RFC 8259. While
     scanning, bytes are escaped and copied into buffer token_buffer. Then the
     function returns successfully, token_buffer is *not* null-terminated (as it
     may contain \0 bytes), and token_buffer.size() is the number of bytes in the
@@ -7227,10 +7357,10 @@ class lexer : public lexer_base<BasicJsonType>
     /*!
     @brief scan a number literal
 
-    This function scans a string according to Sect. 6 of RFC 7159.
+    This function scans a string according to Sect. 6 of RFC 8259.
 
     The function is realized with a deterministic finite state machine derived
-    from the grammar described in RFC 7159. Starting in state "init", the
+    from the grammar described in RFC 8259. Starting in state "init", the
     input is read and used to determined the next state. Only state "done"
     accepts the number. State "error" is a trap state to model errors. In the
     table below, "anything" means any character but the ones listed before.
@@ -17066,8 +17196,8 @@ The invariants are checked by member function assert_invariant().
 @note ObjectType trick from https://stackoverflow.com/a/9860911
 @endinternal
 
-@see [RFC 7159: The JavaScript Object Notation (JSON) Data Interchange
-Format](http://rfc7159.net/rfc7159)
+@see [RFC 8259: The JavaScript Object Notation (JSON) Data Interchange
+Format](https://tools.ietf.org/html/rfc8259)
 
 @since version 1.0.0
 
@@ -17328,7 +17458,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /*!
     @brief a type for an object
 
-    [RFC 7159](http://rfc7159.net/rfc7159) describes JSON objects as follows:
+    [RFC 8259](https://tools.ietf.org/html/rfc8259) describes JSON objects as follows:
     > An object is an unordered collection of zero or more name/value pairs,
     > where a name is a string and a value is a string, number, boolean, null,
     > object, or array.
@@ -17382,7 +17512,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     #### Limits
 
-    [RFC 7159](http://rfc7159.net/rfc7159) specifies:
+    [RFC 8259](https://tools.ietf.org/html/rfc8259) specifies:
     > An implementation may set limits on the maximum depth of nesting.
 
     In this class, the object's limit of nesting is not explicitly constrained.
@@ -17405,7 +17535,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     name/value pairs in a different order than they were originally stored. In
     fact, keys will be traversed in alphabetical order as `std::map` with
     `std::less` is used by default. Please note this behavior conforms to [RFC
-    7159](http://rfc7159.net/rfc7159), because any order implements the
+    8259](https://tools.ietf.org/html/rfc8259), because any order implements the
     specified "unordered" nature of JSON objects.
     */
     using object_t = ObjectType<StringType,
@@ -17417,7 +17547,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /*!
     @brief a type for an array
 
-    [RFC 7159](http://rfc7159.net/rfc7159) describes JSON arrays as follows:
+    [RFC 8259](https://tools.ietf.org/html/rfc8259) describes JSON arrays as follows:
     > An array is an ordered sequence of zero or more values.
 
     To store objects in C++, a type is defined by the template parameters
@@ -17441,7 +17571,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     #### Limits
 
-    [RFC 7159](http://rfc7159.net/rfc7159) specifies:
+    [RFC 8259](https://tools.ietf.org/html/rfc8259) specifies:
     > An implementation may set limits on the maximum depth of nesting.
 
     In this class, the array's limit of nesting is not explicitly constrained.
@@ -17463,7 +17593,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /*!
     @brief a type for a string
 
-    [RFC 7159](http://rfc7159.net/rfc7159) describes JSON strings as follows:
+    [RFC 8259](https://tools.ietf.org/html/rfc8259) describes JSON strings as follows:
     > A string is a sequence of zero or more Unicode characters.
 
     To store objects in C++, a type is defined by the template parameter
@@ -17490,7 +17620,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     #### String comparison
 
-    [RFC 7159](http://rfc7159.net/rfc7159) states:
+    [RFC 8259](https://tools.ietf.org/html/rfc8259) states:
     > Software implementations are typically required to test names of object
     > members for equality. Implementations that transform the textual
     > representation into sequences of Unicode code units and then perform the
@@ -17516,7 +17646,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /*!
     @brief a type for a boolean
 
-    [RFC 7159](http://rfc7159.net/rfc7159) implicitly describes a boolean as a
+    [RFC 8259](https://tools.ietf.org/html/rfc8259) implicitly describes a boolean as a
     type which differentiates the two literals `true` and `false`.
 
     To store objects in C++, a type is defined by the template parameter @a
@@ -17542,7 +17672,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /*!
     @brief a type for a number (integer)
 
-    [RFC 7159](http://rfc7159.net/rfc7159) describes numbers as follows:
+    [RFC 8259](https://tools.ietf.org/html/rfc8259) describes numbers as follows:
     > The representation of numbers is similar to that used in most
     > programming languages. A number is represented in base 10 using decimal
     > digits. It contains an integer component that may be prefixed with an
@@ -17580,7 +17710,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     #### Limits
 
-    [RFC 7159](http://rfc7159.net/rfc7159) specifies:
+    [RFC 8259](https://tools.ietf.org/html/rfc8259) specifies:
     > An implementation may set limits on the range and precision of numbers.
 
     When the default type is used, the maximal integer number that can be
@@ -17591,7 +17721,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     will be automatically be stored as @ref number_unsigned_t or @ref
     number_float_t.
 
-    [RFC 7159](http://rfc7159.net/rfc7159) further states:
+    [RFC 8259](https://tools.ietf.org/html/rfc8259) further states:
     > Note that when such software is used, numbers that are integers and are
     > in the range \f$[-2^{53}+1, 2^{53}-1]\f$ are interoperable in the sense
     > that implementations will agree exactly on their numeric values.
@@ -17614,7 +17744,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /*!
     @brief a type for a number (unsigned)
 
-    [RFC 7159](http://rfc7159.net/rfc7159) describes numbers as follows:
+    [RFC 8259](https://tools.ietf.org/html/rfc8259) describes numbers as follows:
     > The representation of numbers is similar to that used in most
     > programming languages. A number is represented in base 10 using decimal
     > digits. It contains an integer component that may be prefixed with an
@@ -17652,7 +17782,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     #### Limits
 
-    [RFC 7159](http://rfc7159.net/rfc7159) specifies:
+    [RFC 8259](https://tools.ietf.org/html/rfc8259) specifies:
     > An implementation may set limits on the range and precision of numbers.
 
     When the default type is used, the maximal integer number that can be
@@ -17662,7 +17792,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     deserialization, too large or small integer numbers will be automatically
     be stored as @ref number_integer_t or @ref number_float_t.
 
-    [RFC 7159](http://rfc7159.net/rfc7159) further states:
+    [RFC 8259](https://tools.ietf.org/html/rfc8259) further states:
     > Note that when such software is used, numbers that are integers and are
     > in the range \f$[-2^{53}+1, 2^{53}-1]\f$ are interoperable in the sense
     > that implementations will agree exactly on their numeric values.
@@ -17685,7 +17815,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /*!
     @brief a type for a number (floating-point)
 
-    [RFC 7159](http://rfc7159.net/rfc7159) describes numbers as follows:
+    [RFC 8259](https://tools.ietf.org/html/rfc8259) describes numbers as follows:
     > The representation of numbers is similar to that used in most
     > programming languages. A number is represented in base 10 using decimal
     > digits. It contains an integer component that may be prefixed with an
@@ -17723,7 +17853,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     #### Limits
 
-    [RFC 7159](http://rfc7159.net/rfc7159) states:
+    [RFC 8259](https://tools.ietf.org/html/rfc8259) states:
     > This specification allows implementations to set limits on the range and
     > precision of numbers accepted. Since software that implements IEEE
     > 754-2008 binary64 (double precision) numbers is generally available and
@@ -18161,9 +18291,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             }));
         }
         JSON_CATCH(...) {} // LCOV_EXCL_LINE
-#else
-        static_cast<void>(check_parents);
 #endif
+        static_cast<void>(check_parents);
     }
 
     void set_parents()
@@ -19826,50 +19955,53 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// @{
 
     /*!
-    @brief get special-case overload
+    @brief get a pointer value (implicit)
 
-    This overloads avoids a lot of template boilerplate, it can be seen as the
-    identity method
+    Implicit pointer access to the internally stored JSON value. No copies are
+    made.
 
-    @tparam BasicJsonType == @ref basic_json
+    @warning Writing data to the pointee of the result yields an undefined
+    state.
 
-    @return a copy of *this
+    @tparam PointerType pointer type; must be a pointer to @ref array_t, @ref
+    object_t, @ref string_t, @ref boolean_t, @ref number_integer_t,
+    @ref number_unsigned_t, or @ref number_float_t. Enforced by a static
+    assertion.
+
+    @return pointer to the internally stored JSON value if the requested
+    pointer type @a PointerType fits to the JSON value; `nullptr` otherwise
 
     @complexity Constant.
 
-    @since version 2.1.0
+    @liveexample{The example below shows how pointers to internal values of a
+    JSON value can be requested. Note that no type conversions are made and a
+    `nullptr` is returned if the value and the requested pointer type does not
+    match.,get_ptr}
+
+    @since version 1.0.0
     */
-    template<typename BasicJsonType, detail::enable_if_t<
-                 std::is_same<typename std::remove_const<BasicJsonType>::type, basic_json_t>::value,
-                 int> = 0>
-    basic_json get() const
+    template<typename PointerType, typename std::enable_if<
+                 std::is_pointer<PointerType>::value, int>::type = 0>
+    auto get_ptr() noexcept -> decltype(std::declval<basic_json_t&>().get_impl_ptr(std::declval<PointerType>()))
     {
-        return *this;
+        // delegate the call to get_impl_ptr<>()
+        return get_impl_ptr(static_cast<PointerType>(nullptr));
     }
 
     /*!
-    @brief get special-case overload
-
-    This overloads converts the current @ref basic_json in a different
-    @ref basic_json type
-
-    @tparam BasicJsonType == @ref basic_json
-
-    @return a copy of *this, converted into @a BasicJsonType
-
-    @complexity Depending on the implementation of the called `from_json()`
-                method.
-
-    @since version 3.2.0
+    @brief get a pointer value (implicit)
+    @copydoc get_ptr()
     */
-    template < typename BasicJsonType, detail::enable_if_t <
-                   !std::is_same<BasicJsonType, basic_json>::value&&
-                   detail::is_basic_json<BasicJsonType>::value, int > = 0 >
-    BasicJsonType get() const
+    template < typename PointerType, typename std::enable_if <
+                   std::is_pointer<PointerType>::value&&
+                   std::is_const<typename std::remove_pointer<PointerType>::type>::value, int >::type = 0 >
+    constexpr auto get_ptr() const noexcept -> decltype(std::declval<const basic_json_t&>().get_impl_ptr(std::declval<PointerType>()))
     {
-        return *this;
+        // delegate the call to get_impl_ptr<>() const
+        return get_impl_ptr(static_cast<PointerType>(nullptr));
     }
 
+  private:
     /*!
     @brief get a value (explicit)
 
@@ -19893,7 +20025,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     - @ref json_serializer<ValueType> does not have a `from_json()` method of
       the form `ValueType from_json(const basic_json&)`
 
-    @tparam ValueTypeCV the provided value type
     @tparam ValueType the returned value type
 
     @return copy of the JSON value, converted to @a ValueType
@@ -19909,23 +20040,14 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     @since version 2.1.0
     */
-    template < typename ValueTypeCV, typename ValueType = detail::uncvref_t<ValueTypeCV>,
+    template < typename ValueType,
                detail::enable_if_t <
-                   !detail::is_basic_json<ValueType>::value &&
-                   detail::has_from_json<basic_json_t, ValueType>::value &&
-                   !detail::has_non_default_from_json<basic_json_t, ValueType>::value,
+                   detail::is_default_constructible<ValueType>::value&&
+                   detail::has_from_json<basic_json_t, ValueType>::value,
                    int > = 0 >
-    ValueType get() const noexcept(noexcept(
-                                       JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>(), std::declval<ValueType&>())))
+    ValueType get_impl(detail::priority_tag<0> /*unused*/) const noexcept(noexcept(
+                JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>(), std::declval<ValueType&>())))
     {
-        // we cannot static_assert on ValueTypeCV being non-const, because
-        // there is support for get<const basic_json_t>(), which is why we
-        // still need the uncvref
-        static_assert(!std::is_reference<ValueTypeCV>::value,
-                      "get() cannot be used with reference types, you might want to use get_ref()");
-        static_assert(std::is_default_constructible<ValueType>::value,
-                      "types must be DefaultConstructible when used with get()");
-
         ValueType ret{};
         JSONSerializer<ValueType>::from_json(*this, ret);
         return ret;
@@ -19942,7 +20064,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     The function is equivalent to executing
     @code {.cpp}
-    return JSONSerializer<ValueTypeCV>::from_json(*this);
+    return JSONSerializer<ValueType>::from_json(*this);
     @endcode
 
     This overloads is chosen if:
@@ -19953,7 +20075,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     @note If @ref json_serializer<ValueType> has both overloads of
     `from_json()`, this one is chosen.
 
-    @tparam ValueTypeCV the provided value type
     @tparam ValueType the returned value type
 
     @return copy of the JSON value, converted to @a ValueType
@@ -19962,134 +20083,116 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     @since version 2.1.0
     */
-    template < typename ValueTypeCV, typename ValueType = detail::uncvref_t<ValueTypeCV>,
-               detail::enable_if_t < !std::is_same<basic_json_t, ValueType>::value &&
-                                     detail::has_non_default_from_json<basic_json_t, ValueType>::value,
-                                     int > = 0 >
-    ValueType get() const noexcept(noexcept(
-                                       JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>())))
+    template < typename ValueType,
+               detail::enable_if_t <
+                   detail::has_non_default_from_json<basic_json_t, ValueType>::value,
+                   int > = 0 >
+    ValueType get_impl(detail::priority_tag<1> /*unused*/) const noexcept(noexcept(
+                JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>())))
     {
-        static_assert(!std::is_reference<ValueTypeCV>::value,
-                      "get() cannot be used with reference types, you might want to use get_ref()");
         return JSONSerializer<ValueType>::from_json(*this);
     }
 
     /*!
-    @brief get a value (explicit)
-
-    Explicit type conversion between the JSON value and a compatible value.
-    The value is filled into the input parameter by calling the @ref json_serializer<ValueType>
-    `from_json()` method.
-
-    The function is equivalent to executing
-    @code {.cpp}
-    ValueType v;
-    JSONSerializer<ValueType>::from_json(*this, v);
-    @endcode
-
-    This overloads is chosen if:
-    - @a ValueType is not @ref basic_json,
-    - @ref json_serializer<ValueType> has a `from_json()` method of the form
-      `void from_json(const basic_json&, ValueType&)`, and
+    @brief get special-case overload
 
-    @tparam ValueType the input parameter type.
+    This overloads converts the current @ref basic_json in a different
+    @ref basic_json type
 
-    @return the input parameter, allowing chaining calls.
+    @tparam BasicJsonType == @ref basic_json
 
-    @throw what @ref json_serializer<ValueType> `from_json()` method throws
+    @return a copy of *this, converted into @a BasicJsonType
 
-    @liveexample{The example below shows several conversions from JSON values
-    to other types. There a few things to note: (1) Floating-point numbers can
-    be converted to integers\, (2) A JSON array can be converted to a standard
-    `std::vector<short>`\, (3) A JSON object can be converted to C++
-    associative containers such as `std::unordered_map<std::string\,
-    json>`.,get_to}
+    @complexity Depending on the implementation of the called `from_json()`
+                method.
 
-    @since version 3.3.0
+    @since version 3.2.0
     */
-    template < typename ValueType,
+    template < typename BasicJsonType,
                detail::enable_if_t <
-                   !detail::is_basic_json<ValueType>::value&&
-                   detail::has_from_json<basic_json_t, ValueType>::value,
+                   detail::is_basic_json<BasicJsonType>::value,
                    int > = 0 >
-    ValueType & get_to(ValueType& v) const noexcept(noexcept(
-                JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>(), v)))
+    BasicJsonType get_impl(detail::priority_tag<2> /*unused*/) const
     {
-        JSONSerializer<ValueType>::from_json(*this, v);
-        return v;
+        return *this;
     }
 
-    // specialization to allow to call get_to with a basic_json value
-    // see https://github.com/nlohmann/json/issues/2175
-    template<typename ValueType,
-             detail::enable_if_t <
-                 detail::is_basic_json<ValueType>::value,
+    /*!
+    @brief get special-case overload
+
+    This overloads avoids a lot of template boilerplate, it can be seen as the
+    identity method
+
+    @tparam BasicJsonType == @ref basic_json
+
+    @return a copy of *this
+
+    @complexity Constant.
+
+    @since version 2.1.0
+    */
+    template<typename BasicJsonType,
+             detail::enable_if_t<
+                 std::is_same<BasicJsonType, basic_json_t>::value,
                  int> = 0>
-    ValueType & get_to(ValueType& v) const
+    basic_json get_impl(detail::priority_tag<3> /*unused*/) const
     {
-        v = *this;
-        return v;
+        return *this;
     }
 
-    template <
-        typename T, std::size_t N,
-        typename Array = T (&)[N], // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
-        detail::enable_if_t <
-            detail::has_from_json<basic_json_t, Array>::value, int > = 0 >
-    Array get_to(T (&v)[N]) const // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
-    noexcept(noexcept(JSONSerializer<Array>::from_json(
-                          std::declval<const basic_json_t&>(), v)))
+    /*!
+    @brief get a pointer value (explicit)
+    @copydoc get()
+    */
+    template<typename PointerType,
+             detail::enable_if_t<
+                 std::is_pointer<PointerType>::value,
+                 int> = 0>
+    constexpr auto get_impl(detail::priority_tag<4> /*unused*/) const noexcept
+    -> decltype(std::declval<const basic_json_t&>().template get_ptr<PointerType>())
     {
-        JSONSerializer<Array>::from_json(*this, v);
-        return v;
+        // delegate the call to get_ptr
+        return get_ptr<PointerType>();
     }
 
-
+  public:
     /*!
-    @brief get a pointer value (implicit)
+    @brief get a (pointer) value (explicit)
 
-    Implicit pointer access to the internally stored JSON value. No copies are
-    made.
+    Performs explicit type conversion between the JSON value and a compatible value if required.
 
-    @warning Writing data to the pointee of the result yields an undefined
-    state.
+    - If the requested type is a pointer to the internally stored JSON value that pointer is returned.
+    No copies are made.
 
-    @tparam PointerType pointer type; must be a pointer to @ref array_t, @ref
-    object_t, @ref string_t, @ref boolean_t, @ref number_integer_t,
-    @ref number_unsigned_t, or @ref number_float_t. Enforced by a static
-    assertion.
+    - If the requested type is the current @ref basic_json, or a different @ref basic_json convertible
+    from the current @ref basic_json.
 
-    @return pointer to the internally stored JSON value if the requested
-    pointer type @a PointerType fits to the JSON value; `nullptr` otherwise
+    - Otherwise the value is converted by calling the @ref json_serializer<ValueType> `from_json()`
+    method.
 
-    @complexity Constant.
+    @tparam ValueTypeCV the provided value type
+    @tparam ValueType the returned value type
 
-    @liveexample{The example below shows how pointers to internal values of a
-    JSON value can be requested. Note that no type conversions are made and a
-    `nullptr` is returned if the value and the requested pointer type does not
-    match.,get_ptr}
+    @return copy of the JSON value, converted to @tparam ValueType if necessary
 
-    @since version 1.0.0
-    */
-    template<typename PointerType, typename std::enable_if<
-                 std::is_pointer<PointerType>::value, int>::type = 0>
-    auto get_ptr() noexcept -> decltype(std::declval<basic_json_t&>().get_impl_ptr(std::declval<PointerType>()))
-    {
-        // delegate the call to get_impl_ptr<>()
-        return get_impl_ptr(static_cast<PointerType>(nullptr));
-    }
+    @throw what @ref json_serializer<ValueType> `from_json()` method throws if conversion is required
 
-    /*!
-    @brief get a pointer value (implicit)
-    @copydoc get_ptr()
+    @since version 2.1.0
     */
-    template < typename PointerType, typename std::enable_if <
-                   std::is_pointer<PointerType>::value&&
-                   std::is_const<typename std::remove_pointer<PointerType>::type>::value, int >::type = 0 >
-    constexpr auto get_ptr() const noexcept -> decltype(std::declval<const basic_json_t&>().get_impl_ptr(std::declval<PointerType>()))
+    template < typename ValueTypeCV, typename ValueType = detail::uncvref_t<ValueTypeCV>>
+#if defined(JSON_HAS_CPP_14)
+    constexpr
+#endif
+    auto get() const noexcept(
+    noexcept(std::declval<const basic_json_t&>().template get_impl<ValueType>(detail::priority_tag<4> {})))
+    -> decltype(std::declval<const basic_json_t&>().template get_impl<ValueType>(detail::priority_tag<4> {}))
     {
-        // delegate the call to get_impl_ptr<>() const
-        return get_impl_ptr(static_cast<PointerType>(nullptr));
+        // we cannot static_assert on ValueTypeCV being non-const, because
+        // there is support for get<const basic_json_t>(), which is why we
+        // still need the uncvref
+        static_assert(!std::is_reference<ValueTypeCV>::value,
+                      "get() cannot be used with reference types, you might want to use get_ref()");
+        return get_impl<ValueType>(detail::priority_tag<4> {});
     }
 
     /*!
@@ -20128,15 +20231,73 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     }
 
     /*!
-    @brief get a pointer value (explicit)
-    @copydoc get()
+    @brief get a value (explicit)
+
+    Explicit type conversion between the JSON value and a compatible value.
+    The value is filled into the input parameter by calling the @ref json_serializer<ValueType>
+    `from_json()` method.
+
+    The function is equivalent to executing
+    @code {.cpp}
+    ValueType v;
+    JSONSerializer<ValueType>::from_json(*this, v);
+    @endcode
+
+    This overloads is chosen if:
+    - @a ValueType is not @ref basic_json,
+    - @ref json_serializer<ValueType> has a `from_json()` method of the form
+      `void from_json(const basic_json&, ValueType&)`, and
+
+    @tparam ValueType the input parameter type.
+
+    @return the input parameter, allowing chaining calls.
+
+    @throw what @ref json_serializer<ValueType> `from_json()` method throws
+
+    @liveexample{The example below shows several conversions from JSON values
+    to other types. There a few things to note: (1) Floating-point numbers can
+    be converted to integers\, (2) A JSON array can be converted to a standard
+    `std::vector<short>`\, (3) A JSON object can be converted to C++
+    associative containers such as `std::unordered_map<std::string\,
+    json>`.,get_to}
+
+    @since version 3.3.0
     */
-    template<typename PointerType, typename std::enable_if<
-                 std::is_pointer<PointerType>::value, int>::type = 0>
-    constexpr auto get() const noexcept -> decltype(std::declval<const basic_json_t&>().template get_ptr<PointerType>())
+    template < typename ValueType,
+               detail::enable_if_t <
+                   !detail::is_basic_json<ValueType>::value&&
+                   detail::has_from_json<basic_json_t, ValueType>::value,
+                   int > = 0 >
+    ValueType & get_to(ValueType& v) const noexcept(noexcept(
+                JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>(), v)))
     {
-        // delegate the call to get_ptr
-        return get_ptr<PointerType>();
+        JSONSerializer<ValueType>::from_json(*this, v);
+        return v;
+    }
+
+    // specialization to allow to call get_to with a basic_json value
+    // see https://github.com/nlohmann/json/issues/2175
+    template<typename ValueType,
+             detail::enable_if_t <
+                 detail::is_basic_json<ValueType>::value,
+                 int> = 0>
+    ValueType & get_to(ValueType& v) const
+    {
+        v = *this;
+        return v;
+    }
+
+    template <
+        typename T, std::size_t N,
+        typename Array = T (&)[N], // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
+        detail::enable_if_t <
+            detail::has_from_json<basic_json_t, Array>::value, int > = 0 >
+    Array get_to(T (&v)[N]) const // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
+    noexcept(noexcept(JSONSerializer<Array>::from_json(
+                          std::declval<const basic_json_t&>(), v)))
+    {
+        JSONSerializer<Array>::from_json(*this, v);
+        return v;
     }
 
     /*!
@@ -25755,8 +25916,10 @@ inline nlohmann::json::json_pointer operator "" _json_pointer(const char* s, std
 #undef JSON_THROW
 #undef JSON_TRY
 #undef JSON_PRIVATE_UNLESS_TESTED
+#undef JSON_HAS_CPP_11
 #undef JSON_HAS_CPP_14
 #undef JSON_HAS_CPP_17
+#undef JSON_HAS_CPP_20
 #undef NLOHMANN_BASIC_JSON_TPL_DECLARATION
 #undef NLOHMANN_BASIC_JSON_TPL
 #undef JSON_EXPLICIT