mirror of
https://github.com/nlohmann/json.git
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454 lines
17 KiB
C++
454 lines
17 KiB
C++
#pragma once
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#include <limits> // numeric_limits
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#include <type_traits> // false_type, is_constructible, is_integral, is_same, true_type
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#include <utility> // declval
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#include <tuple> // tuple
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#include <nlohmann/detail/iterators/iterator_traits.hpp>
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#include <nlohmann/detail/macro_scope.hpp>
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#include <nlohmann/detail/meta/cpp_future.hpp>
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#include <nlohmann/detail/meta/detected.hpp>
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#include <nlohmann/json_fwd.hpp>
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namespace nlohmann
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{
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/*!
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@brief detail namespace with internal helper functions
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This namespace collects functions that should not be exposed,
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implementations of some @ref basic_json methods, and meta-programming helpers.
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@since version 2.1.0
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*/
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namespace detail
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{
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/////////////
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// helpers //
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/////////////
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// Note to maintainers:
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//
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// Every trait in this file expects a non CV-qualified type.
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// The only exceptions are in the 'aliases for detected' section
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// (i.e. those of the form: decltype(T::member_function(std::declval<T>())))
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//
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// In this case, T has to be properly CV-qualified to constraint the function arguments
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// (e.g. to_json(BasicJsonType&, const T&))
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template<typename> struct is_basic_json : std::false_type {};
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NLOHMANN_BASIC_JSON_TPL_DECLARATION
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struct is_basic_json<NLOHMANN_BASIC_JSON_TPL> : std::true_type {};
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//////////////////////
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// json_ref helpers //
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//////////////////////
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template<typename>
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class json_ref;
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template<typename>
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struct is_json_ref : std::false_type {};
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template<typename T>
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struct is_json_ref<json_ref<T>> : std::true_type {};
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//////////////////////////
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// aliases for detected //
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//////////////////////////
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template<typename T>
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using mapped_type_t = typename T::mapped_type;
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template<typename T>
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using key_type_t = typename T::key_type;
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template<typename T>
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using value_type_t = typename T::value_type;
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template<typename T>
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using difference_type_t = typename T::difference_type;
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template<typename T>
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using pointer_t = typename T::pointer;
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template<typename T>
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using reference_t = typename T::reference;
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template<typename T>
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using iterator_category_t = typename T::iterator_category;
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template<typename T>
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using iterator_t = typename T::iterator;
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template<typename T, typename... Args>
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using to_json_function = decltype(T::to_json(std::declval<Args>()...));
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template<typename T, typename... Args>
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using from_json_function = decltype(T::from_json(std::declval<Args>()...));
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template<typename T, typename U>
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using get_template_function = decltype(std::declval<T>().template get<U>());
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// trait checking if JSONSerializer<T>::from_json(json const&, udt&) exists
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template<typename BasicJsonType, typename T, typename = void>
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struct has_from_json : std::false_type {};
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// trait checking if j.get<T> is valid
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// use this trait instead of std::is_constructible or std::is_convertible,
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// both rely on, or make use of implicit conversions, and thus fail when T
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// has several constructors/operator= (see https://github.com/nlohmann/json/issues/958)
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template <typename BasicJsonType, typename T>
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struct is_getable
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{
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static constexpr bool value = is_detected<get_template_function, const BasicJsonType&, T>::value;
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};
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template<typename BasicJsonType, typename T>
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struct has_from_json < BasicJsonType, T, enable_if_t < !is_basic_json<T>::value >>
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{
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using serializer = typename BasicJsonType::template json_serializer<T, void>;
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static constexpr bool value =
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is_detected_exact<void, from_json_function, serializer,
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const BasicJsonType&, T&>::value;
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};
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// This trait checks if JSONSerializer<T>::from_json(json const&) exists
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// this overload is used for non-default-constructible user-defined-types
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template<typename BasicJsonType, typename T, typename = void>
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struct has_non_default_from_json : std::false_type {};
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template<typename BasicJsonType, typename T>
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struct has_non_default_from_json < BasicJsonType, T, enable_if_t < !is_basic_json<T>::value >>
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{
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using serializer = typename BasicJsonType::template json_serializer<T, void>;
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static constexpr bool value =
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is_detected_exact<T, from_json_function, serializer,
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const BasicJsonType&>::value;
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};
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// This trait checks if BasicJsonType::json_serializer<T>::to_json exists
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// Do not evaluate the trait when T is a basic_json type, to avoid template instantiation infinite recursion.
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template<typename BasicJsonType, typename T, typename = void>
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struct has_to_json : std::false_type {};
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template<typename BasicJsonType, typename T>
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struct has_to_json < BasicJsonType, T, enable_if_t < !is_basic_json<T>::value >>
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{
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using serializer = typename BasicJsonType::template json_serializer<T, void>;
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static constexpr bool value =
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is_detected_exact<void, to_json_function, serializer, BasicJsonType&,
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T>::value;
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};
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///////////////////
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// is_ functions //
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///////////////////
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// https://en.cppreference.com/w/cpp/types/conjunction
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template<class...> struct conjunction : std::true_type { };
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template<class B1> struct conjunction<B1> : B1 { };
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template<class B1, class... Bn>
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struct conjunction<B1, Bn...>
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: std::conditional<bool(B1::value), conjunction<Bn...>, B1>::type {};
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// https://en.cppreference.com/w/cpp/types/negation
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template<class B> struct negation : std::integral_constant < bool, !B::value > { };
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// Reimplementation of is_constructible and is_default_constructible, due to them being broken for
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// std::pair and std::tuple until LWG 2367 fix (see https://cplusplus.github.io/LWG/lwg-defects.html#2367).
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// This causes compile errors in e.g. clang 3.5 or gcc 4.9.
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template <typename T>
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struct is_default_constructible : std::is_default_constructible<T> {};
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template <typename T1, typename T2>
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struct is_default_constructible<std::pair<T1, T2>>
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: conjunction<is_default_constructible<T1>, is_default_constructible<T2>> {};
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template <typename T1, typename T2>
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struct is_default_constructible<const std::pair<T1, T2>>
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: conjunction<is_default_constructible<T1>, is_default_constructible<T2>> {};
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template <typename... Ts>
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struct is_default_constructible<std::tuple<Ts...>>
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: conjunction<is_default_constructible<Ts>...> {};
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template <typename... Ts>
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struct is_default_constructible<const std::tuple<Ts...>>
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: conjunction<is_default_constructible<Ts>...> {};
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template <typename T, typename... Args>
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struct is_constructible : std::is_constructible<T, Args...> {};
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template <typename T1, typename T2>
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struct is_constructible<std::pair<T1, T2>> : is_default_constructible<std::pair<T1, T2>> {};
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template <typename T1, typename T2>
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struct is_constructible<const std::pair<T1, T2>> : is_default_constructible<const std::pair<T1, T2>> {};
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template <typename... Ts>
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struct is_constructible<std::tuple<Ts...>> : is_default_constructible<std::tuple<Ts...>> {};
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template <typename... Ts>
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struct is_constructible<const std::tuple<Ts...>> : is_default_constructible<const std::tuple<Ts...>> {};
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template<typename T, typename = void>
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struct is_iterator_traits : std::false_type {};
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template<typename T>
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struct is_iterator_traits<iterator_traits<T>>
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{
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private:
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using traits = iterator_traits<T>;
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public:
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static constexpr auto value =
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is_detected<value_type_t, traits>::value &&
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is_detected<difference_type_t, traits>::value &&
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is_detected<pointer_t, traits>::value &&
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is_detected<iterator_category_t, traits>::value &&
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is_detected<reference_t, traits>::value;
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};
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// The following implementation of is_complete_type is taken from
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// https://blogs.msdn.microsoft.com/vcblog/2015/12/02/partial-support-for-expression-sfinae-in-vs-2015-update-1/
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// and is written by Xiang Fan who agreed to using it in this library.
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template<typename T, typename = void>
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struct is_complete_type : std::false_type {};
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template<typename T>
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struct is_complete_type<T, decltype(void(sizeof(T)))> : std::true_type {};
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template<typename BasicJsonType, typename CompatibleObjectType,
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typename = void>
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struct is_compatible_object_type_impl : std::false_type {};
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template<typename BasicJsonType, typename CompatibleObjectType>
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struct is_compatible_object_type_impl <
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BasicJsonType, CompatibleObjectType,
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enable_if_t < is_detected<mapped_type_t, CompatibleObjectType>::value&&
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is_detected<key_type_t, CompatibleObjectType>::value >>
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{
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using object_t = typename BasicJsonType::object_t;
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// macOS's is_constructible does not play well with nonesuch...
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static constexpr bool value =
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is_constructible<typename object_t::key_type,
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typename CompatibleObjectType::key_type>::value &&
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is_constructible<typename object_t::mapped_type,
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typename CompatibleObjectType::mapped_type>::value;
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};
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template<typename BasicJsonType, typename CompatibleObjectType>
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struct is_compatible_object_type
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: is_compatible_object_type_impl<BasicJsonType, CompatibleObjectType> {};
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template<typename BasicJsonType, typename ConstructibleObjectType,
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typename = void>
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struct is_constructible_object_type_impl : std::false_type {};
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template<typename BasicJsonType, typename ConstructibleObjectType>
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struct is_constructible_object_type_impl <
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BasicJsonType, ConstructibleObjectType,
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enable_if_t < is_detected<mapped_type_t, ConstructibleObjectType>::value&&
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is_detected<key_type_t, ConstructibleObjectType>::value >>
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{
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using object_t = typename BasicJsonType::object_t;
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static constexpr bool value =
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(is_default_constructible<ConstructibleObjectType>::value &&
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(std::is_move_assignable<ConstructibleObjectType>::value ||
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std::is_copy_assignable<ConstructibleObjectType>::value) &&
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(is_constructible<typename ConstructibleObjectType::key_type,
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typename object_t::key_type>::value &&
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std::is_same <
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typename object_t::mapped_type,
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typename ConstructibleObjectType::mapped_type >::value)) ||
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(has_from_json<BasicJsonType,
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typename ConstructibleObjectType::mapped_type>::value ||
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has_non_default_from_json <
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BasicJsonType,
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typename ConstructibleObjectType::mapped_type >::value);
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};
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template<typename BasicJsonType, typename ConstructibleObjectType>
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struct is_constructible_object_type
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: is_constructible_object_type_impl<BasicJsonType,
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ConstructibleObjectType> {};
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template<typename BasicJsonType, typename CompatibleStringType,
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typename = void>
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struct is_compatible_string_type_impl : std::false_type {};
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template<typename BasicJsonType, typename CompatibleStringType>
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struct is_compatible_string_type_impl <
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BasicJsonType, CompatibleStringType,
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enable_if_t<is_detected_exact<typename BasicJsonType::string_t::value_type,
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value_type_t, CompatibleStringType>::value >>
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{
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static constexpr auto value =
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is_constructible<typename BasicJsonType::string_t, CompatibleStringType>::value;
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};
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template<typename BasicJsonType, typename ConstructibleStringType>
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struct is_compatible_string_type
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: is_compatible_string_type_impl<BasicJsonType, ConstructibleStringType> {};
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template<typename BasicJsonType, typename ConstructibleStringType,
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typename = void>
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struct is_constructible_string_type_impl : std::false_type {};
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template<typename BasicJsonType, typename ConstructibleStringType>
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struct is_constructible_string_type_impl <
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BasicJsonType, ConstructibleStringType,
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enable_if_t<is_detected_exact<typename BasicJsonType::string_t::value_type,
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value_type_t, ConstructibleStringType>::value >>
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{
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static constexpr auto value =
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is_constructible<ConstructibleStringType,
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typename BasicJsonType::string_t>::value;
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};
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template<typename BasicJsonType, typename ConstructibleStringType>
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struct is_constructible_string_type
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: is_constructible_string_type_impl<BasicJsonType, ConstructibleStringType> {};
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template<typename BasicJsonType, typename CompatibleArrayType, typename = void>
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struct is_compatible_array_type_impl : std::false_type {};
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template<typename BasicJsonType, typename CompatibleArrayType>
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struct is_compatible_array_type_impl <
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BasicJsonType, CompatibleArrayType,
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enable_if_t < is_detected<value_type_t, CompatibleArrayType>::value&&
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is_detected<iterator_t, CompatibleArrayType>::value&&
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// This is needed because json_reverse_iterator has a ::iterator type...
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// Therefore it is detected as a CompatibleArrayType.
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// The real fix would be to have an Iterable concept.
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!is_iterator_traits <
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iterator_traits<CompatibleArrayType >>::value >>
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{
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static constexpr bool value =
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is_constructible<BasicJsonType,
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typename CompatibleArrayType::value_type>::value;
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};
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template<typename BasicJsonType, typename CompatibleArrayType>
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struct is_compatible_array_type
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: is_compatible_array_type_impl<BasicJsonType, CompatibleArrayType> {};
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template<typename BasicJsonType, typename ConstructibleArrayType, typename = void>
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struct is_constructible_array_type_impl : std::false_type {};
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template<typename BasicJsonType, typename ConstructibleArrayType>
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struct is_constructible_array_type_impl <
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BasicJsonType, ConstructibleArrayType,
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enable_if_t<std::is_same<ConstructibleArrayType,
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typename BasicJsonType::value_type>::value >>
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: std::true_type {};
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template<typename BasicJsonType, typename ConstructibleArrayType>
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struct is_constructible_array_type_impl <
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BasicJsonType, ConstructibleArrayType,
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enable_if_t < !std::is_same<ConstructibleArrayType,
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typename BasicJsonType::value_type>::value&&
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is_default_constructible<ConstructibleArrayType>::value&&
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(std::is_move_assignable<ConstructibleArrayType>::value ||
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std::is_copy_assignable<ConstructibleArrayType>::value)&&
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is_detected<value_type_t, ConstructibleArrayType>::value&&
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is_detected<iterator_t, ConstructibleArrayType>::value&&
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is_complete_type <
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detected_t<value_type_t, ConstructibleArrayType >>::value >>
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{
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static constexpr bool value =
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// This is needed because json_reverse_iterator has a ::iterator type,
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// furthermore, std::back_insert_iterator (and other iterators) have a
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// base class `iterator`... Therefore it is detected as a
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// ConstructibleArrayType. The real fix would be to have an Iterable
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// concept.
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!is_iterator_traits<iterator_traits<ConstructibleArrayType>>::value &&
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(std::is_same<typename ConstructibleArrayType::value_type,
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typename BasicJsonType::array_t::value_type>::value ||
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has_from_json<BasicJsonType,
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typename ConstructibleArrayType::value_type>::value ||
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has_non_default_from_json <
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BasicJsonType, typename ConstructibleArrayType::value_type >::value);
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};
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template<typename BasicJsonType, typename ConstructibleArrayType>
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struct is_constructible_array_type
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: is_constructible_array_type_impl<BasicJsonType, ConstructibleArrayType> {};
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template<typename RealIntegerType, typename CompatibleNumberIntegerType,
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typename = void>
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struct is_compatible_integer_type_impl : std::false_type {};
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template<typename RealIntegerType, typename CompatibleNumberIntegerType>
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struct is_compatible_integer_type_impl <
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RealIntegerType, CompatibleNumberIntegerType,
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enable_if_t < std::is_integral<RealIntegerType>::value&&
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std::is_integral<CompatibleNumberIntegerType>::value&&
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!std::is_same<bool, CompatibleNumberIntegerType>::value >>
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{
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// is there an assert somewhere on overflows?
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using RealLimits = std::numeric_limits<RealIntegerType>;
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using CompatibleLimits = std::numeric_limits<CompatibleNumberIntegerType>;
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static constexpr auto value =
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is_constructible<RealIntegerType,
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CompatibleNumberIntegerType>::value &&
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CompatibleLimits::is_integer &&
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RealLimits::is_signed == CompatibleLimits::is_signed;
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};
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template<typename RealIntegerType, typename CompatibleNumberIntegerType>
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struct is_compatible_integer_type
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: is_compatible_integer_type_impl<RealIntegerType,
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CompatibleNumberIntegerType> {};
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template<typename BasicJsonType, typename CompatibleType, typename = void>
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struct is_compatible_type_impl: std::false_type {};
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template<typename BasicJsonType, typename CompatibleType>
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struct is_compatible_type_impl <
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BasicJsonType, CompatibleType,
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enable_if_t<is_complete_type<CompatibleType>::value >>
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{
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static constexpr bool value =
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has_to_json<BasicJsonType, CompatibleType>::value;
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};
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template<typename BasicJsonType, typename CompatibleType>
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struct is_compatible_type
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: is_compatible_type_impl<BasicJsonType, CompatibleType> {};
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template<typename T1, typename T2>
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struct is_constructible_tuple : std::false_type {};
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template<typename T1, typename... Args>
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struct is_constructible_tuple<T1, std::tuple<Args...>> : conjunction<is_constructible<T1, Args>...> {};
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// to avoid useless casts (see https://github.com/nlohmann/json/issues/2893#issuecomment-889152324)
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template < typename T, typename U, enable_if_t < !std::is_same<T, U>::value, int > = 0 >
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T conditional_static_cast(U value)
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{
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return static_cast<T>(value);
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}
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template<typename T, typename U, enable_if_t<std::is_same<T, U>::value, int> = 0>
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T conditional_static_cast(U value)
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{
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return value;
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}
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} // namespace detail
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} // namespace nlohmann
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