IntegerSequence.hpp

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#ifndef ESTD_INTEGERSEQUENCE_HPP_
#define ESTD_INTEGERSEQUENCE_HPP_

#include <type_traits>

namespace estd
{

template<typename T, T... Integers>
class IntegerSequence
{
public:

    using value_type = T;

    constexpr static std::size_t size() noexcept
    {
        return sizeof...(Integers);
    };
};

template<std::size_t... Indexes>
using IndexSequence = IntegerSequence<std::size_t, Indexes...>;

namespace internal
{

template<typename T, T... Integers>
struct TypedSequence : IntegerSequence<T, Integers...>
{
    using base = IntegerSequence<T, Integers...>;

    using type = TypedSequence;
};

template<typename Sequence>
struct DoubledIntegerSequence;

template<typename T, T... Integers>
struct DoubledIntegerSequence<TypedSequence<T, Integers...>>
{
    using type = TypedSequence<T, Integers..., (sizeof...(Integers) + Integers)...>;
};

template<bool Extend, typename Sequence>
struct ExtendedIntegerSequence
{
    using type = Sequence;
};

template<typename T, T... Integers>
struct ExtendedIntegerSequence<true, TypedSequence<T, Integers...>>
{
    using type = TypedSequence<T, Integers..., sizeof...(Integers)>;
};

template<typename T, std::size_t N>
struct MakeIntegerSequenceImplementation :
        ExtendedIntegerSequence<N % 2 != 0,
                typename DoubledIntegerSequence<typename MakeIntegerSequenceImplementation<T, N / 2>::type>::type>
{

};

template<typename T>
struct MakeIntegerSequenceImplementation<T, 0>
{
    using type = TypedSequence<T>;
};

template<typename T, T N>
struct MakeIntegerSequenceImplementationWrapper :
        std::enable_if<N >= 0, MakeIntegerSequenceImplementation<T, static_cast<std::size_t>(N)>>::type
{
    static_assert(N >= 0, "Number of elements in the sequence must be non-negative!");
};

}   // namespace internal

template<typename T, T N>
using MakeIntegerSequence = typename internal::MakeIntegerSequenceImplementationWrapper<T, N>::type::base;

template<std::size_t N>
using MakeIndexSequence = MakeIntegerSequence<std::size_t, N>;

template<typename... T>
using IndexSequenceFor = MakeIndexSequence<sizeof...(T)>;

}   // namespace estd

#endif  // ESTD_INTEGERSEQUENCE_HPP_