Less.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreTypes.h"
#include "Concepts/SameAs.h"
#include "UnrealTemplate.h"
 
template <typename T /*= void */>
struct TLess
{
    [[nodiscard]] UE_REWRITE constexpr bool operator()(const T& A, const T& B) const
    {
        if constexpr (requires { { A < B } -> UE::CSameAs<bool>; })
        {
            return A < B;
        }
        else
        {
            static_assert(sizeof(T) == 0, "Trying to use TLess<T> where T doesn't have an appropriate operator< overload. Please add bool operator<(T, T), do not specialize TLess.");
        }
    }
};
 
template <>
struct TLess<void>
{
    template <typename T, typename U>
    [[nodiscard]] UE_REWRITE constexpr bool operator()(T&& A, U&& B) const
    {
        if constexpr (requires { { Forward<T>(A) < Forward<U>(B) } -> UE::CSameAs<bool>; })
        {
            return Forward<T>(A) < Forward<U>(B);
        }
        else
        {
            static_assert(sizeof(T) == 0, "Trying to use TLess<void> with types without an appropriate operator< overload. Please add bool operator<(T, U), do not specialize TLess.");
        }
    }
};