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155 lines
4.4 KiB
C++
155 lines
4.4 KiB
C++
#pragma once
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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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#include <utility> // index_sequence, make_index_sequence, index_sequence_for
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#include <nlohmann/detail/macro_scope.hpp>
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namespace nlohmann
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{
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namespace detail
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{
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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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#ifdef JSON_HAS_CPP_14
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// the following utilities are natively available in C++14
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using std::enable_if_t;
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using std::index_sequence;
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using std::make_index_sequence;
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using std::index_sequence_for;
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#else
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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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// The following code is taken from https://github.com/abseil/abseil-cpp/blob/10cb35e459f5ecca5b2ff107635da0bfa41011b4/absl/utility/utility.h
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// which is part of Google Abseil (https://github.com/abseil/abseil-cpp), licensed under the Apache License 2.0.
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//// START OF CODE FROM GOOGLE ABSEIL
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// integer_sequence
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//
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// Class template representing a compile-time integer sequence. An instantiation
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// of `integer_sequence<T, Ints...>` has a sequence of integers encoded in its
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// type through its template arguments (which is a common need when
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// working with C++11 variadic templates). `absl::integer_sequence` is designed
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// to be a drop-in replacement for C++14's `std::integer_sequence`.
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//
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// Example:
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//
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// template< class T, T... Ints >
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// void user_function(integer_sequence<T, Ints...>);
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//
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// int main()
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// {
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// // user_function's `T` will be deduced to `int` and `Ints...`
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// // will be deduced to `0, 1, 2, 3, 4`.
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// user_function(make_integer_sequence<int, 5>());
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// }
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template <typename T, T... Ints>
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struct integer_sequence
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{
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using value_type = 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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// index_sequence
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//
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// A helper template for an `integer_sequence` of `size_t`,
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// `absl::index_sequence` is designed to be a drop-in replacement for C++14's
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// `std::index_sequence`.
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template <size_t... Ints>
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using index_sequence = integer_sequence<size_t, Ints...>;
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namespace utility_internal
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{
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template <typename Seq, size_t SeqSize, size_t Rem>
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struct Extend;
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// Note that SeqSize == sizeof...(Ints). It's passed explicitly for efficiency.
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template <typename T, T... Ints, size_t SeqSize>
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struct Extend<integer_sequence<T, Ints...>, SeqSize, 0>
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{
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using type = integer_sequence < T, Ints..., (Ints + SeqSize)... >;
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};
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template <typename T, T... Ints, size_t SeqSize>
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struct Extend<integer_sequence<T, Ints...>, SeqSize, 1>
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{
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using type = integer_sequence < T, Ints..., (Ints + SeqSize)..., 2 * SeqSize >;
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};
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// Recursion helper for 'make_integer_sequence<T, N>'.
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// 'Gen<T, N>::type' is an alias for 'integer_sequence<T, 0, 1, ... N-1>'.
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template <typename T, size_t N>
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struct Gen
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{
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using type =
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typename Extend < typename Gen < T, N / 2 >::type, N / 2, N % 2 >::type;
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};
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template <typename T>
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struct Gen<T, 0>
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{
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using type = integer_sequence<T>;
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};
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} // namespace utility_internal
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// Compile-time sequences of integers
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// make_integer_sequence
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//
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// This template alias is equivalent to
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// `integer_sequence<int, 0, 1, ..., N-1>`, and is designed to be a drop-in
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// replacement for C++14's `std::make_integer_sequence`.
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template <typename T, T N>
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using make_integer_sequence = typename utility_internal::Gen<T, N>::type;
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// make_index_sequence
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//
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// This template alias is equivalent to `index_sequence<0, 1, ..., N-1>`,
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// and is designed to be a drop-in replacement for C++14's
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// `std::make_index_sequence`.
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template <size_t N>
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using make_index_sequence = make_integer_sequence<size_t, N>;
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// index_sequence_for
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//
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// Converts a typename pack into an index sequence of the same length, and
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// is designed to be a drop-in replacement for C++14's
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// `std::index_sequence_for()`
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template <typename... Ts>
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using index_sequence_for = make_index_sequence<sizeof...(Ts)>;
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//// END OF CODE FROM GOOGLE ABSEIL
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#endif
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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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} // namespace detail
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} // namespace nlohmann
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