feat(templates): add TRetainedRef and the corresponding testing

Redcraft.Utility/Source/Public/Templates/RetainedReference.h

@@ -0,0 +1,73 @@
+#pragma once
+
+#include "CoreTypes.h"
+#include "Templates/Utility.h"
+#include "TypeTraits/TypeTraits.h"
+
+NAMESPACE_REDCRAFT_BEGIN
+NAMESPACE_MODULE_BEGIN(Redcraft)
+NAMESPACE_MODULE_BEGIN(Utility)
+
+/**
+ * A helper class which replaces T& as a function parameter when the reference is
+ * intended to be retained by the function (e.g. as a class member).  The benefit
+ * of this class is that it is a compile error to pass an rvalue which might otherwise
+ * bind to a const reference, which is dangerous when the reference is retained.
+ *
+ *	struct FRAIIType
+ *	{
+ *		explicit FRAIIType(TRetainedRef<const FThing> InThing) : Ref(InThing) { }
+ *
+ *		void DoSomething() { Ref.Something(); }
+ *
+ *		FThing& Ref;
+ *	};
+ *
+ */
+template <typename T>
+struct TRetainedRef
+{
+	/** Retain a non-const lvalue reference. */
+	FORCEINLINE constexpr TRetainedRef(T& InRef) : Ref(InRef) { }
+
+	/** Can't retain a rvalue reference. */
+	TRetainedRef(const T& ) = delete;
+	TRetainedRef(      T&&) = delete;
+	TRetainedRef(const T&&) = delete;
+
+	/** @return The managed reference. */
+	FORCEINLINE constexpr operator T&() const { return Ref; }
+	FORCEINLINE constexpr      T& Get() const { return Ref; }
+
+private:
+
+	T& Ref;
+
+};
+
+template <typename T>
+struct TRetainedRef<const T>
+{
+	/** Retain a non-const lvalue reference. */
+	FORCEINLINE constexpr TRetainedRef(T& InRef) : Ref(InRef) { }
+
+	/** Retain a const lvalue reference. */
+	FORCEINLINE constexpr TRetainedRef(const T& InRef) : Ref(InRef) { }
+
+	/** Can't retain a rvalue reference. */
+	TRetainedRef(      T&&) = delete;
+	TRetainedRef(const T&&) = delete;
+
+	/** @return The managed reference. */
+	FORCEINLINE constexpr operator const T&() const { return Ref; }
+	FORCEINLINE constexpr      const T& Get() const { return Ref; }
+
+private:
+
+	const T& Ref;
+
+};
+
+NAMESPACE_MODULE_END(Utility)
+NAMESPACE_MODULE_END(Redcraft)
+NAMESPACE_REDCRAFT_END

Redcraft.Utility/Source/Public/Templates/Templates.h

@@ -16,3 +16,4 @@
 #include "Templates/Atomic.h"
 #include "Templates/ScopeHelper.h"
 #include "Templates/PropagateConst.h"
+#include "Templates/RetainedReference.h"