84 lines
2.7 KiB
C++
84 lines
2.7 KiB
C++
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#pragma once
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#include <ciso646> // not
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#include <cstddef> // size_t
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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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namespace nlohmann
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{
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namespace detail
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{
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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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// 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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