HasGetTypeHash.h

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// Copyright 1998-2017 Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "AndOrNot.h"
#include "IsArithmetic.h"
#include "IsPointer.h"
#include "IsEnum.h"
 
namespace UE4GetTypeHashExists_Private
{
    struct FNotSpecified {};
 
    template <typename T>
    struct FReturnValueCheck
    {
        static char (&Func())[2];
    };
 
    template <>
    struct FReturnValueCheck<FNotSpecified>
    {
        static char (&Func())[1];
    };
 
    template <typename T>
    FNotSpecified GetTypeHash(const T&);
 
    template <typename T>
    const T& Make();
 
    template <typename T, bool bIsHashableScalarType = TOr<TIsArithmetic<T>, TIsPointer<T>, TIsEnum<T>>::Value>
    struct GetTypeHashQuery
    {
        // All arithmetic, pointer and enums types are hashable
        enum { Value = true };
    };
 
    template <typename T>
    struct GetTypeHashQuery<T, false>
    {
        enum { Value = sizeof(FReturnValueCheck<decltype(GetTypeHash(Make<T>()))>::Func()) == sizeof(char[2]) };
    };
}
 
/**
* Traits class which tests if a type has a GetTypeHash overload.
*/
template <typename T>
struct THasGetTypeHash
{
    enum { Value = UE4GetTypeHashExists_Private::GetTypeHashQuery<T>::Value };
};