Implementation of a C++17 feature - `std::apply` - in C++11 standard

future_apply.hh

/*
Implementation of a C++17 feature - `std::apply` - in C++11 standard
*/

#ifndef FUTURE_APPLY_HH
#define FUTURE_APPLY_HH

#include <tuple>
#include <utility>
#include <type_traits>

namespace future
{

template<size_t...>
struct IndexSequence
{
};

template<size_t... integers>
struct _MakeIndexSequence;

template<size_t counter, size_t... integers>
struct _MakeIndexSequence<counter, integers...>
{
    using Type = typename _MakeIndexSequence<counter - 1, counter - 1, integers...>::Type;
};

template<size_t... integers>
struct _MakeIndexSequence<0, integers...>
{
    using Type = IndexSequence<integers...>;
};

template<typename Tuple>
struct _IndexSequenceForTuple
{
    using Type = typename _MakeIndexSequence<std::tuple_size<typename std::remove_reference<Tuple>::type>::value>::Type;
};

template<typename Tuple>
using IndexSequenceForTuple = typename _IndexSequenceForTuple<Tuple>::Type;

template<typename Function, typename Tuple, size_t... Index>
auto _Apply(Function && function, Tuple && tuple, IndexSequence<Index...>) -> decltype(function(std::get<Index>(std::forward<Tuple>(tuple))...))
{
    return std::forward<Function>(function)(std::get<Index>(std::forward<Tuple>(tuple))...);
}

template<typename Function, typename Tuple>
auto Apply(Function && function, Tuple && tuple) -> decltype(_Apply(std::forward<Function>(function), std::forward<Tuple>(tuple), IndexSequenceForTuple<Tuple>()))
{
    return _Apply(std::forward<Function>(function), std::forward<Tuple>(tuple), IndexSequenceForTuple<Tuple>());
}

}

#endif // FUTURE_APPLY_HH