mirror of
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235 lines
8.4 KiB
C++
235 lines
8.4 KiB
C++
#pragma once
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#include <ciso646> // not
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#include <cstddef> // size_t
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#include <limits> // numeric_limits
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#include <type_traits> // conditional, enable_if, false_type, integral_constant, is_constructible, is_integral, is_same, remove_cv, remove_reference, true_type
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#include <utility> // declval
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#include "json_fwd.hpp"
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#include "detail/macro_scope.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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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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// alias templates to reduce boilerplate
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template<bool B, typename T = void>
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using enable_if_t = typename std::enable_if<B, T>::type;
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template<typename T>
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using uncvref_t = typename std::remove_cv<typename std::remove_reference<T>::type>::type;
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// implementation of C++14 index_sequence and affiliates
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// source: https://stackoverflow.com/a/32223343
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template<std::size_t... Ints>
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struct index_sequence
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{
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using type = index_sequence;
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using value_type = std::size_t;
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static constexpr std::size_t size() noexcept
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{
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return sizeof...(Ints);
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}
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};
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template<class Sequence1, class Sequence2>
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struct merge_and_renumber;
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template<std::size_t... I1, std::size_t... I2>
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struct merge_and_renumber<index_sequence<I1...>, index_sequence<I2...>>
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: index_sequence < I1..., (sizeof...(I1) + I2)... > {};
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template<std::size_t N>
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struct make_index_sequence
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: merge_and_renumber < typename make_index_sequence < N / 2 >::type,
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typename make_index_sequence < N - N / 2 >::type > {};
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template<> struct make_index_sequence<0> : index_sequence<> {};
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template<> struct make_index_sequence<1> : index_sequence<0> {};
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template<typename... Ts>
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using index_sequence_for = make_index_sequence<sizeof...(Ts)>;
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/*
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Implementation of two C++17 constructs: conjunction, negation. This is needed
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to avoid evaluating all the traits in a condition
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For example: not std::is_same<void, T>::value and has_value_type<T>::value
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will not compile when T = void (on MSVC at least). Whereas
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conjunction<negation<std::is_same<void, T>>, has_value_type<T>>::value will
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stop evaluating if negation<...>::value == false
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Please note that those constructs must be used with caution, since symbols can
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become very long quickly (which can slow down compilation and cause MSVC
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internal compiler errors). Only use it when you have to (see example ahead).
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*/
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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...> : std::conditional<bool(B1::value), conjunction<Bn...>, B1>::type {};
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template<class B> struct negation : std::integral_constant<bool, not B::value> {};
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// dispatch utility (taken from ranges-v3)
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template<unsigned N> struct priority_tag : priority_tag < N - 1 > {};
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template<> struct priority_tag<0> {};
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////////////////////////
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// has_/is_ functions //
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////////////////////////
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NLOHMANN_JSON_HAS_HELPER(mapped_type);
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NLOHMANN_JSON_HAS_HELPER(key_type);
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NLOHMANN_JSON_HAS_HELPER(value_type);
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NLOHMANN_JSON_HAS_HELPER(iterator);
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template<bool B, class RealType, class CompatibleObjectType>
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struct is_compatible_object_type_impl : std::false_type {};
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template<class RealType, class CompatibleObjectType>
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struct is_compatible_object_type_impl<true, RealType, CompatibleObjectType>
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{
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static constexpr auto value =
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std::is_constructible<typename RealType::key_type, typename CompatibleObjectType::key_type>::value and
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std::is_constructible<typename RealType::mapped_type, typename CompatibleObjectType::mapped_type>::value;
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};
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template<class BasicJsonType, class CompatibleObjectType>
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struct is_compatible_object_type
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{
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static auto constexpr value = is_compatible_object_type_impl <
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conjunction<negation<std::is_same<void, CompatibleObjectType>>,
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has_mapped_type<CompatibleObjectType>,
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has_key_type<CompatibleObjectType>>::value,
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typename BasicJsonType::object_t, CompatibleObjectType >::value;
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};
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template<typename BasicJsonType, typename T>
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struct is_basic_json_nested_type
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{
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static auto constexpr value = std::is_same<T, typename BasicJsonType::iterator>::value or
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std::is_same<T, typename BasicJsonType::const_iterator>::value or
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std::is_same<T, typename BasicJsonType::reverse_iterator>::value or
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std::is_same<T, typename BasicJsonType::const_reverse_iterator>::value;
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};
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template<class BasicJsonType, class CompatibleArrayType>
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struct is_compatible_array_type
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{
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static auto constexpr value =
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conjunction<negation<std::is_same<void, CompatibleArrayType>>,
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negation<is_compatible_object_type<
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BasicJsonType, CompatibleArrayType>>,
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negation<std::is_constructible<typename BasicJsonType::string_t,
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CompatibleArrayType>>,
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negation<is_basic_json_nested_type<BasicJsonType, CompatibleArrayType>>,
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has_value_type<CompatibleArrayType>,
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has_iterator<CompatibleArrayType>>::value;
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};
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template<bool, typename, typename>
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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<true, RealIntegerType, CompatibleNumberIntegerType>
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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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std::is_constructible<RealIntegerType, CompatibleNumberIntegerType>::value and
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CompatibleLimits::is_integer and
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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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{
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static constexpr auto value =
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is_compatible_integer_type_impl <
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std::is_integral<CompatibleNumberIntegerType>::value and
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not std::is_same<bool, CompatibleNumberIntegerType>::value,
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RealIntegerType, CompatibleNumberIntegerType > ::value;
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};
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// trait checking if JSONSerializer<T>::from_json(json const&, udt&) exists
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template<typename BasicJsonType, typename T>
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struct has_from_json
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{
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private:
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// also check the return type of from_json
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template<typename U, typename = enable_if_t<std::is_same<void, decltype(uncvref_t<U>::from_json(
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std::declval<BasicJsonType>(), std::declval<T&>()))>::value>>
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static int detect(U&&);
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static void detect(...);
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public:
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static constexpr bool value = std::is_integral<decltype(
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detect(std::declval<typename BasicJsonType::template json_serializer<T, void>>()))>::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>
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struct has_non_default_from_json
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{
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private:
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template <
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typename U,
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typename = enable_if_t<std::is_same<
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T, decltype(uncvref_t<U>::from_json(std::declval<BasicJsonType>()))>::value >>
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static int detect(U&&);
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static void detect(...);
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public:
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static constexpr bool value = std::is_integral<decltype(detect(
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std::declval<typename BasicJsonType::template json_serializer<T, void>>()))>::value;
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};
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// This trait checks if BasicJsonType::json_serializer<T>::to_json exists
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template<typename BasicJsonType, typename T>
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struct has_to_json
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{
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private:
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template<typename U, typename = decltype(uncvref_t<U>::to_json(
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std::declval<BasicJsonType&>(), std::declval<T>()))>
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static int detect(U&&);
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static void detect(...);
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public:
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static constexpr bool value = std::is_integral<decltype(detect(
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std::declval<typename BasicJsonType::template json_serializer<T, void>>()))>::value;
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};
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// taken from ranges-v3
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template<typename T>
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struct static_const
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{
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static constexpr T value{};
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};
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template<typename T>
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constexpr T static_const<T>::value;
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}
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}
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