IntegerSequence.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreTypes.h"
 
template <typename T, T... Indices>
struct TIntegerSequence
{
};
 
#ifdef _MSC_VER
 
template <typename T, T N>
using TMakeIntegerSequence = __make_integer_seq<TIntegerSequence, T, N>;
 
#elif __has_builtin(__make_integer_seq)
 
template <typename T, T N>
using TMakeIntegerSequence = __make_integer_seq<TIntegerSequence, T, N>;
 
#else
 
namespace UE4IntegerSequence_Private
{
    template <typename T, unsigned N>
    struct TMakeIntegerSequenceImpl;
}
 
template <typename T, T N>
using TMakeIntegerSequence = typename UE4IntegerSequence_Private::TMakeIntegerSequenceImpl<T, N>::Type;
 
    // Doxygen can't parse recursive template definitions; just skip it.
    #if !UE_BUILD_DOCS
 
    namespace UE4IntegerSequence_Private
    {
        template<unsigned N, typename T1, typename T2>
        struct TConcatImpl;
 
        template<unsigned N, typename T, T... Indices1, T... Indices2>
        struct TConcatImpl<N, TIntegerSequence<T, Indices1...>, TIntegerSequence<T, Indices2...>> : TIntegerSequence<T, Indices1..., (T(N + Indices2))...>
        {
            using Type = TIntegerSequence<T, Indices1..., (T(N + Indices2))...>;
        };
 
        template<unsigned N, typename T1, typename T2>
        using TConcat = typename TConcatImpl<N, T1, T2>::Type;
 
        template <typename T, unsigned N>
        struct TMakeIntegerSequenceImpl : TConcat<N / 2, TMakeIntegerSequence<T, N / 2>, TMakeIntegerSequence<T, N - N / 2>>
        {
            using Type = TConcat<N / 2, TMakeIntegerSequence<T, N / 2>, TMakeIntegerSequence<T, N - N / 2>>;
        };
 
        template <typename T>
        struct TMakeIntegerSequenceImpl<T, 1> : TIntegerSequence<T, T(0)> 
        {
            using Type = TIntegerSequence<T, T(0)>;
        };
 
        template <typename T>
        struct TMakeIntegerSequenceImpl<T, 0> : TIntegerSequence<T> 
        {
            using Type = TIntegerSequence<T>;
        };
    };
 
    #endif
#endif