C++模板应用示例

2020/12 21 12:12
// microsoft stl

// STRUCT TEMPLATE remove_reference
template <class _Ty>
struct remove_reference {
    using type                 = _Ty;
    using _Const_thru_ref_type = const _Ty;
};

template <class _Ty>
struct remove_reference<_Ty&> {
    using type                 = _Ty;
    using _Const_thru_ref_type = const _Ty&;
};

template <class _Ty>
struct remove_reference<_Ty&&> {
    using type                 = _Ty;
    using _Const_thru_ref_type = const _Ty&&;
};

template <class _Ty>
using remove_reference_t = typename remove_reference<_Ty>::type;



// epic unreal 

/**
 * TRemoveReference<type> will remove any references from a type.
 */
template <typename T> struct TRemoveReference      { typedef T Type; };
template <typename T> struct TRemoveReference<T& > { typedef T Type; };
template <typename T> struct TRemoveReference<T&&> { typedef T Type; };

/**
 * Removes one level of pointer from a type, e.g.:
 *
 * TRemovePointer<      int32  >::Type == int32
 * TRemovePointer<      int32* >::Type == int32
 * TRemovePointer<      int32**>::Type == int32*
 * TRemovePointer<const int32* >::Type == const int32
 */
template <typename T> struct TRemovePointer     { typedef T Type; };
template <typename T> struct TRemovePointer<T*> { typedef T Type; };

/**
 * MoveTemp will cast a reference to an rvalue reference.
 * This is UE's equivalent of std::move except that it will not compile when passed an rvalue or
 * const object, because we would prefer to be informed when MoveTemp will have no effect.
 */
template <typename T>
FORCEINLINE typename TRemoveReference<T>::Type&& MoveTemp(T&& Obj)
{
	typedef typename TRemoveReference<T>::Type CastType;

	// Validate that we're not being passed an rvalue or a const object - the former is redundant, the latter is almost certainly a mistake
	static_assert(TIsLValueReferenceType<T>::Value, "MoveTemp called on an rvalue");
	static_assert(!TAreTypesEqual<CastType&, const CastType&>::Value, "MoveTemp called on a const object");

	return (CastType&&)Obj;
}

/**
 * MoveTemp will cast a reference to an rvalue reference.
 * This is UE's equivalent of std::move.  It doesn't static assert like MoveTemp, because it is useful in
 * templates or macros where it's not obvious what the argument is, but you want to take advantage of move semantics
 * where you can but not stop compilation.
 */
template <typename T>
FORCEINLINE typename TRemoveReference<T>::Type&& MoveTempIfPossible(T&& Obj)
{
	typedef typename TRemoveReference<T>::Type CastType;
	return (CastType&&)Obj;
}

--转载请注明: http://blog.coolcoding.cn/?p=2956