style(templates): redefine placeholders such as ForceInit, InPlace, etc.

Redcraft.Utility/Source/Public/Miscellaneous/CoreDefines.h

@@ -41,11 +41,6 @@ NAMESPACE_MODULE_BEGIN(Utility)
 enum { INDEX_NONE = -1 };
 enum { UNICODE_BOM = 0xfeff };
 
-enum EForceInit { ForceInit };
-enum ENoInit    { NoInit    };
-enum EInvalid   { Invalid   };
-enum EInPlace   { InPlace   };
-
 NAMESPACE_MODULE_END(Utility)
 NAMESPACE_MODULE_END(Redcraft)
 NAMESPACE_REDCRAFT_END

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

@@ -2,6 +2,7 @@
 
 #include "CoreTypes.h"
 #include "Templates/Compare.h"
+#include "Templates/Placeholders.h"
 #include "Concepts/Comparable.h"
 #include "TypeTraits/TypeTraits.h"
 #include "Miscellaneous/AssertionMacros.h"
@@ -19,17 +20,17 @@ public:
 
 	constexpr TOptional() : bIsValid(false) { }
 
-	constexpr TOptional(EInvalid) : TOptional() { }
+	constexpr TOptional(FInvalid) : TOptional() { }
 
 	template <typename... Types> requires TIsConstructible<OptionalType, Types...>::Value
-	constexpr explicit TOptional(EInPlace, Types&&... Args)
+	constexpr explicit TOptional(FInPlace, Types&&... Args)
 		: bIsValid(true)
 	{
 		new(&Value) OptionalType(Forward<Types>(Args)...);
 	}
 
 	template <typename T = OptionalType> requires TIsConstructible<OptionalType, T&&>::Value
-		&& (!TIsSame<typename TRemoveCVRef<T>::Type, EInPlace>::Value) && (!TIsSame<typename TRemoveCVRef<T>::Type, TOptional>::Value)
+		&& (!TIsSame<typename TRemoveCVRef<T>::Type, FInPlace>::Value) && (!TIsSame<typename TRemoveCVRef<T>::Type, TOptional>::Value)
 	constexpr explicit(!TIsConvertible<T&&, OptionalType>::Value) TOptional(T&& InValue)
 		: TOptional(InPlace, Forward<T>(InValue))
 	{ }
@@ -250,6 +251,12 @@ constexpr bool operator!=(const T& LHS, const TOptional<U>& RHS)
 	return RHS.IsValid() ? LHS != *RHS : true;
 }
 
+template <typename T>
+constexpr TOptional<typename TDecay<T>::Type> MakeOptional(FInvalid)
+{
+	return TOptional<typename TDecay<T>::Type>(Invalid);
+}
+
 template <typename T>
 constexpr TOptional<typename TDecay<T>::Type> MakeOptional(T&& InValue)
 {

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

@@ -0,0 +1,29 @@
+#pragma once
+
+#include "CoreTypes.h"
+
+NAMESPACE_REDCRAFT_BEGIN
+NAMESPACE_MODULE_BEGIN(Redcraft)
+NAMESPACE_MODULE_BEGIN(Utility)
+
+struct FForceInit { explicit FForceInit() = default; };
+inline constexpr FForceInit ForceInit{};
+
+struct FNoInit { explicit FNoInit() = default; };
+inline constexpr FNoInit NoInit{};
+
+struct FInvalid { explicit FInvalid() = default; };
+inline constexpr FInvalid Invalid{};
+
+struct FInPlace { explicit FInPlace() = default; };
+inline constexpr FInPlace InPlace{};
+
+template <typename T> struct TInPlaceType { explicit TInPlaceType() = default; };
+template <typename T> inline constexpr TInPlaceType<T> InPlaceType{};
+
+template <size_t I> struct TInPlaceIndex { explicit TInPlaceIndex() = default; };
+template <size_t I> inline constexpr TInPlaceIndex<I> InPlaceIndex{};
+
+NAMESPACE_MODULE_END(Utility)
+NAMESPACE_MODULE_END(Redcraft)
+NAMESPACE_REDCRAFT_END

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

@@ -2,6 +2,7 @@
 
 #include "CoreTypes.h"
 #include "Templates/Utility.h"
+#include "Templates/Placeholders.h"
 #include "Templates/Container.h"
 #include "Templates/Noncopyable.h"
 #include "Templates/Invoke.h"