PointerIsConvertibleFromTo.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreTypes.h"
#include "Misc/StaticAssertCompleteType.h"
#include "Templates/LosesQualifiersFromTo.h"
#include <type_traits>
 
namespace UE::Core::Private::PointerIsConvertibleFromTo
{
    template <typename From, typename To, typename NoCVFrom = std::remove_cv_t<From>, typename NoCVTo = std::remove_cv_t<To>>
    struct TImpl
    {
    private:
        static uint8  Test(...);
        static uint16 Test(To*);
 
        UE_STATIC_ASSERT_COMPLETE_TYPE(From, "TPointerIsConvertibleFromTo must not be instantiated with incomplete types");
        UE_STATIC_ASSERT_COMPLETE_TYPE(To,   "TPointerIsConvertibleFromTo must not be instantiated with incomplete types");
 
    public:
        enum { Value = sizeof(Test((From*)nullptr)) - 1 };
    };
 
    template <typename From, typename To, typename NoCVFrom>
    struct TImpl<From, To, NoCVFrom, NoCVFrom>
    {
        // cv T* to cv T* conversions are always allowed as long as no CVs are lost
        enum { Value = !TLosesQualifiersFromTo_V<From, To> };
    };
 
    template <typename From, typename To, typename NoCVFrom>
    struct TImpl<From, To, NoCVFrom, void>
    {
        // cv T* to cv void* conversions are always allowed as long as no CVs are lost
        enum { Value = !TLosesQualifiersFromTo_V<From, To> };
    };
 
    template <typename From, typename To>
    struct TImpl<From, To, void, void>
    {
        // cv void* to cv void* conversions are always allowed as long as no CVs are lost
        enum { Value = !TLosesQualifiersFromTo_V<From, To> };
    };
 
    template <typename From, typename To, typename NoCVTo>
    struct TImpl<From, To, void, NoCVTo>
    {
        // cv void* to cv not_void* conversions are never legal
        enum { Value = false };
    };
}
 
template <typename From, typename To>
struct TPointerIsConvertibleFromTo : UE::Core::Private::PointerIsConvertibleFromTo::TImpl<From, To>
{
};
 
 
class TPointerIsConvertibleFromTo_TestBase
{
};
 
class TPointerIsConvertibleFromTo_TestDerived : public TPointerIsConvertibleFromTo_TestBase
{
};
 
class TPointerIsConvertibleFromTo_Unrelated
{
};
 
static_assert(TPointerIsConvertibleFromTo<bool, bool>::Value, "Platform TPointerIsConvertibleFromTo test failed.");
static_assert(TPointerIsConvertibleFromTo<void, void>::Value, "Platform TPointerIsConvertibleFromTo test failed.");
static_assert(TPointerIsConvertibleFromTo<bool, void>::Value, "Platform TPointerIsConvertibleFromTo test failed.");
static_assert(TPointerIsConvertibleFromTo<const bool, const void>::Value, "Platform TPointerIsConvertibleFromTo test failed.");
static_assert(TPointerIsConvertibleFromTo<TPointerIsConvertibleFromTo_TestDerived, TPointerIsConvertibleFromTo_TestBase>::Value, "Platform TPointerIsConvertibleFromTo test failed.");
static_assert(TPointerIsConvertibleFromTo<TPointerIsConvertibleFromTo_TestDerived, const TPointerIsConvertibleFromTo_TestBase>::Value, "Platform TPointerIsConvertibleFromTo test failed.");
static_assert(TPointerIsConvertibleFromTo<const TPointerIsConvertibleFromTo_TestDerived, const TPointerIsConvertibleFromTo_TestBase>::Value, "Platform TPointerIsConvertibleFromTo test failed.");
static_assert(TPointerIsConvertibleFromTo<TPointerIsConvertibleFromTo_TestBase, TPointerIsConvertibleFromTo_TestBase>::Value, "Platform TPointerIsConvertibleFromTo test failed.");
static_assert(TPointerIsConvertibleFromTo<TPointerIsConvertibleFromTo_TestBase, void>::Value, "Platform TPointerIsConvertibleFromTo test failed.");
 
static_assert(!TPointerIsConvertibleFromTo<TPointerIsConvertibleFromTo_TestBase, TPointerIsConvertibleFromTo_TestDerived>::Value, "Platform TPointerIsConvertibleFromTo test failed.");
static_assert(!TPointerIsConvertibleFromTo<TPointerIsConvertibleFromTo_Unrelated, TPointerIsConvertibleFromTo_TestBase>::Value, "Platform TPointerIsConvertibleFromTo test failed.");
static_assert(!TPointerIsConvertibleFromTo<bool, TPointerIsConvertibleFromTo_TestBase>::Value, "Platform TPointerIsConvertibleFromTo test failed.");
static_assert(!TPointerIsConvertibleFromTo<void, TPointerIsConvertibleFromTo_TestBase>::Value, "Platform TPointerIsConvertibleFromTo test failed.");
static_assert(!TPointerIsConvertibleFromTo<TPointerIsConvertibleFromTo_TestBase, bool>::Value, "Platform TPointerIsConvertibleFromTo test failed.");
static_assert(!TPointerIsConvertibleFromTo<void, bool>::Value, "Platform TPointerIsConvertibleFromTo test failed.");