cpp_future.hpp

#pragma once

#include <cstddef> // size_t
#include <type_traits> // conditional, enable_if, false_type, integral_constant, is_constructible, is_integral, is_same, remove_cv, remove_reference, true_type
#include <utility> // index_sequence, make_index_sequence, index_sequence_for

#include <nlohmann/detail/macro_scope.hpp>

namespace nlohmann
{
namespace detail
{

template<typename T>
using uncvref_t = typename std::remove_cv<typename std::remove_reference<T>::type>::type;

#ifdef JSON_HAS_CPP_14

// the following utilities are natively available in C++14
using std::enable_if_t;
using std::index_sequence;
using std::make_index_sequence;
using std::index_sequence_for;

#else

// alias templates to reduce boilerplate
template<bool B, typename T = void>
using enable_if_t = typename std::enable_if<B, T>::type;

// source: https://stackoverflow.com/a/32223343
template<std::size_t... Ints>
struct index_sequence
{
    using type = index_sequence;
    using value_type = std::size_t;
    static constexpr std::size_t size() noexcept
    {
        return sizeof...(Ints);
    }
};

template<class Sequence1, class Sequence2>
struct merge_and_renumber;

template<std::size_t... I1, std::size_t... I2>
struct merge_and_renumber<index_sequence<I1...>, index_sequence<I2...>>
        : index_sequence < I1..., (sizeof...(I1) + I2)... > {};

template<std::size_t N>
struct make_index_sequence
    : merge_and_renumber < typename make_index_sequence < N / 2 >::type,
      typename make_index_sequence < N - N / 2 >::type > {};

template<> struct make_index_sequence<0> : index_sequence<> {};
template<> struct make_index_sequence<1> : index_sequence<0> {};

template<typename... Ts>
using index_sequence_for = make_index_sequence<sizeof...(Ts)>;

#endif

// dispatch utility (taken from ranges-v3)
template<unsigned N> struct priority_tag : priority_tag < N - 1 > {};
template<> struct priority_tag<0> {};

// taken from ranges-v3
template<typename T>
struct static_const
{
    static constexpr T value{};
};

template<typename T>
constexpr T static_const<T>::value;

}  // namespace detail
}  // namespace nlohmann