From 01eec5d4c0bdf229ba13caf52ea3f6295b2f68e7 Mon Sep 17 00:00:00 2001
From: _Redstone_c_ <myredstone1024@gmail.com>
Date: Sat, 3 Dec 2022 23:11:05 +0800
Subject: [PATCH] feat(templates): add TTypeSequence and meta tools

---
 .../Source/Public/Templates/Function.h        |   4 +-
 .../Source/Public/Templates/IntegerSequence.h |  66 -----
 .../Source/Public/Templates/Meta.h            | 280 ++++++++++++++++++
 .../Source/Public/Templates/Templates.h       |   2 +-
 .../Source/Public/Templates/Tuple.h           |  73 +----
 .../Source/Public/Templates/Utility.h         |  17 ++
 .../Source/Public/Templates/Variant.h         |  82 +----
 .../Source/Public/TypeTraits/Common.h         |   2 +-
 8 files changed, 325 insertions(+), 201 deletions(-)
 delete mode 100644 Redcraft.Utility/Source/Public/Templates/IntegerSequence.h
 create mode 100644 Redcraft.Utility/Source/Public/Templates/Meta.h

diff --git a/Redcraft.Utility/Source/Public/Templates/Function.h b/Redcraft.Utility/Source/Public/Templates/Function.h
index b7bc1e8..8949180 100644
--- a/Redcraft.Utility/Source/Public/Templates/Function.h
+++ b/Redcraft.Utility/Source/Public/Templates/Function.h
@@ -2,7 +2,7 @@
 
 #include "CoreTypes.h"
 #include "Templates/Any.h"
-#include "Templates/Tuple.h"
+#include "Templates/Meta.h"
 #include "Templates/Invoke.h"
 #include "Memory/Alignment.h"
 #include "Templates/Utility.h"
@@ -88,7 +88,7 @@ class TFunctionImpl<Ret(Ts...), CVRef, bIsRef>
 public:
 
 	using ResultType = Ret;
-	using ArgumentType = TTuple<Ts...>;
+	using ArgumentType = TTypeSequence<Ts...>;
 	
 	TFunctionImpl() = default;
 	TFunctionImpl(const TFunctionImpl&) = default;
diff --git a/Redcraft.Utility/Source/Public/Templates/IntegerSequence.h b/Redcraft.Utility/Source/Public/Templates/IntegerSequence.h
deleted file mode 100644
index 3a6bf9a..0000000
--- a/Redcraft.Utility/Source/Public/Templates/IntegerSequence.h
+++ /dev/null
@@ -1,66 +0,0 @@
-#pragma once
-
-#include "CoreTypes.h"
-
-NAMESPACE_REDCRAFT_BEGIN
-NAMESPACE_MODULE_BEGIN(Redcraft)
-NAMESPACE_MODULE_BEGIN(Utility)
-
-template <typename T, T... Ints>
-struct TIntegerSequence 
-{
-	using ValueType = T;
-	static constexpr size_t Size() { return sizeof...(Ints); }
-};
-
-NAMESPACE_PRIVATE_BEGIN
-
-#ifdef _MSC_VER
-
-template <unsigned N, typename T>
-struct TMakeIntegerSequenceImpl
-{
-	using Type = typename __make_integer_seq<TIntegerSequence, T, N>;
-};
-
-#elif __has_builtin(__make_integer_seq)
-
-template <unsigned N, typename T>
-struct TMakeIntegerSequenceImpl
-{
-	using Type = typename __make_integer_seq<TIntegerSequence, T, N>;
-};
-
-#else
-
-template <unsigned N, typename T, T... Ints>
-struct TMakeIntegerSequenceImpl
-{
-	using Type = typename TMakeIntegerSequenceImpl<N - 1, T, T(N - 1), Ints...>::Type;
-};
-
-template <typename T, T... Ints>
-struct TMakeIntegerSequenceImpl<0, T, Ints...>
-{
-	using Type = TIntegerSequence<T, Ints...>;
-};
-
-#endif
-
-NAMESPACE_PRIVATE_END
-
-template <size_t... Ints>
-using TIndexSequence = TIntegerSequence<size_t, Ints...>;
-
-template<typename T, T N>
-using TMakeIntegerSequence = typename NAMESPACE_PRIVATE::TMakeIntegerSequenceImpl<N, T>::Type;
-
-template<size_t N>
-using TMakeIndexSequence = TMakeIntegerSequence<size_t, N>;
-
-template<typename... T>
-using TIndexSequenceFor = TMakeIndexSequence<sizeof...(T)>;
-
-NAMESPACE_MODULE_END(Utility)
-NAMESPACE_MODULE_END(Redcraft)
-NAMESPACE_REDCRAFT_END
diff --git a/Redcraft.Utility/Source/Public/Templates/Meta.h b/Redcraft.Utility/Source/Public/Templates/Meta.h
new file mode 100644
index 0000000..4f7d879
--- /dev/null
+++ b/Redcraft.Utility/Source/Public/Templates/Meta.h
@@ -0,0 +1,280 @@
+#pragma once
+
+#include "CoreTypes.h"
+#include "Templates/Utility.h"
+#include "Templates/Container.h"
+#include "TypeTraits/TypeTraits.h"
+
+NAMESPACE_REDCRAFT_BEGIN
+NAMESPACE_MODULE_BEGIN(Redcraft)
+NAMESPACE_MODULE_BEGIN(Utility)
+
+template <typename T, T... Ints>
+struct TIntegerSequence 
+{
+	using ValueType = T;
+	static constexpr size_t   Num()     { return sizeof...(Ints);                          }
+	static constexpr const T* GetData() { return NAMESPACE_REDCRAFT::GetData({ Ints... }); }
+};
+
+NAMESPACE_PRIVATE_BEGIN
+
+#ifdef _MSC_VER
+
+template <unsigned N, typename T>
+struct TMakeIntegerSequenceImpl
+{
+	using Type = typename __make_integer_seq<TIntegerSequence, T, N>;
+};
+
+#elif __has_builtin(__make_integer_seq)
+
+template <unsigned N, typename T>
+struct TMakeIntegerSequenceImpl
+{
+	using Type = typename __make_integer_seq<TIntegerSequence, T, N>;
+};
+
+#else
+
+template <unsigned N, typename T, T... Ints>
+struct TMakeIntegerSequenceImpl
+{
+	using Type = typename TMakeIntegerSequenceImpl<N - 1, T, T(N - 1), Ints...>::Type;
+};
+
+template <typename T, T... Ints>
+struct TMakeIntegerSequenceImpl<0, T, Ints...>
+{
+	using Type = TIntegerSequence<T, Ints...>;
+};
+
+#endif
+
+NAMESPACE_PRIVATE_END
+
+template <size_t... Ints>
+using TIndexSequence = TIntegerSequence<size_t, Ints...>;
+
+template <typename T, T N>
+using TMakeIntegerSequence = typename NAMESPACE_PRIVATE::TMakeIntegerSequenceImpl<N, T>::Type;
+
+template <size_t N>
+using TMakeIndexSequence = TMakeIntegerSequence<size_t, N>;
+
+template <typename... Ts>
+using TIndexSequenceFor = TMakeIndexSequence<sizeof...(Ts)>;
+
+template <typename... Ts>
+struct TTypeSequence { };
+
+NAMESPACE_PRIVATE_BEGIN
+
+template <typename T           > struct TIsTIntegerSequence                               : FFalse { };
+template <typename T, T... Ints> struct TIsTIntegerSequence<TIntegerSequence<T, Ints...>> : FTrue  { };
+
+template <typename  T   > struct TIsTIndexSequence                          : FFalse { };
+template <size_t... Ints> struct TIsTIndexSequence<TIndexSequence<Ints...>> : FTrue  { };
+
+template <typename    T > struct TIsTTypeSequence                       : FFalse { };
+template <typename... Ts> struct TIsTTypeSequence<TTypeSequence<Ts...>> : FTrue  { };
+
+NAMESPACE_PRIVATE_END
+
+// Unlike other places such as CTTuple, cv-qualifiers are not ignored here
+// This is done to simplify the logic and make it easier to use it
+
+template <typename T>
+concept CTIntegerSequence = NAMESPACE_PRIVATE::TIsTIntegerSequence<T>::Value;
+
+template <typename T>
+concept CTIndexSequence = NAMESPACE_PRIVATE::TIsTIndexSequence<T>::Value;
+
+template <typename T>
+concept CTTypeSequence = NAMESPACE_PRIVATE::TIsTTypeSequence<T>::Value;
+
+NAMESPACE_BEGIN(Meta)
+
+NAMESPACE_PRIVATE_BEGIN
+
+template <typename TSequence>
+struct TFrontImpl;
+
+template <typename T, typename... Ts>
+struct TFrontImpl<TTypeSequence<T, Ts...>>
+{
+	using Type = T;
+};
+
+template <typename TSequence>
+struct TPopImpl;
+
+template <typename T, typename... Ts>
+struct TPopImpl<TTypeSequence<T, Ts...>>
+{
+	using Type = TTypeSequence<Ts...>;
+};
+
+template <typename T, typename TSequence>
+struct TPushImpl;
+
+template <typename T, typename... Ts>
+struct TPushImpl<T, TTypeSequence<Ts...>>
+{
+	using Type = TTypeSequence<T, Ts...>;
+};
+
+NAMESPACE_PRIVATE_END
+
+template <CTTypeSequence TSequence>
+using TFront = typename NAMESPACE_PRIVATE::TFrontImpl<TSequence>::Type;
+
+template <CTTypeSequence TSequence>
+using TPop = typename NAMESPACE_PRIVATE::TPopImpl<TSequence>::Type;
+
+template <typename T, typename TSequence>
+using TPush = typename NAMESPACE_PRIVATE::TPushImpl<T, TSequence>::Type;
+
+NAMESPACE_PRIVATE_BEGIN
+
+template <typename T, typename TSequence>
+struct TTypeCountImpl
+{
+	static constexpr size_t Value = (CSameAs<T, TFront<TSequence>> ? 1 : 0) + TTypeCountImpl<T, TPop<TSequence>>::Value;
+};
+
+template <typename T>
+struct TTypeCountImpl<T, TTypeSequence<>>
+{
+	static constexpr size_t Value = 0;
+};
+
+NAMESPACE_PRIVATE_END
+
+template <typename T, CTTypeSequence TSequence>
+inline constexpr size_t TTypeCount = NAMESPACE_PRIVATE::TTypeCountImpl<T, TSequence>::Value;
+
+template <typename T, typename TSequence>
+concept CExistentType = CTTypeSequence<TSequence> && TTypeCount<T, TSequence> > 0;
+
+template <typename T, typename TSequence>
+concept CDuplicateType = CTTypeSequence<TSequence> && TTypeCount<T, TSequence> > 1;
+
+NAMESPACE_PRIVATE_BEGIN
+
+template <typename TSequence>
+struct TSizeImpl;
+
+template <typename... Ts>
+struct TSizeImpl<TTypeSequence<Ts...>>
+{
+	static constexpr size_t Value = sizeof...(Ts);
+};
+
+template <size_t I, typename T, typename TSequence>
+struct TIndexImpl
+{
+	static constexpr size_t Value = CSameAs<T, TFront<TSequence>> ? I : TIndexImpl<I + 1, T, TPop<TSequence>>::Value;
+};
+
+template <size_t I, typename T>
+struct TIndexImpl<I, T, TTypeSequence<>>
+{
+	static constexpr size_t Value = INDEX_NONE;
+};
+
+template <typename T, typename TSequence>
+struct TIndexAssert
+{
+	static_assert( Meta::CExistentType< T, TSequence>, "T is non-existent types in type sequence");
+	static_assert(!Meta::CDuplicateType<T, TSequence>, "T is duplicate type in type sequence"    );
+	static constexpr size_t Value = TIndexImpl<0, T, TSequence>::Value;
+};
+
+template <size_t I, typename TSequence>
+struct TTypeImpl
+{
+	using Type = typename TTypeImpl<I - 1, TPop<TSequence>>::Type;
+};
+
+template <typename TSequence>
+struct TTypeImpl<0, TSequence>
+{
+	using Type = TFront<TSequence>;
+};
+
+template <typename TSequence>
+struct TTypeImpl<INDEX_NONE, TSequence>
+{
+	using Type = void;
+};
+
+template <size_t I, typename TSequence>
+struct TTypeAssert
+{
+	static_assert(I < TSizeImpl<TSequence>::Value, "I is invalid index in type sequence");
+	static constexpr size_t SafeIndex = I < TSizeImpl<TSequence>::Value ? I : INDEX_NONE;
+	using Type = TCopyCV<TSequence, typename TTypeImpl<SafeIndex, TSequence>::Type>;
+};
+
+NAMESPACE_PRIVATE_END
+
+template <CTTypeSequence TSequence>
+inline constexpr size_t TSize = NAMESPACE_PRIVATE::TSizeImpl<TSequence>::Value;
+
+template <typename T, CTTypeSequence TSequence>
+inline constexpr size_t TIndex = NAMESPACE_PRIVATE::TIndexAssert<T, TSequence>::Value;
+
+template <size_t I, CTTypeSequence TSequence>
+using TType = typename NAMESPACE_PRIVATE::TTypeAssert<I, TSequence>::Type;
+
+NAMESPACE_PRIVATE_BEGIN
+
+template <typename TSequence>
+struct TUniqueTypeSequenceImpl
+{
+	using FrontType = TFront<TSequence>;
+	using NextSequence = TPop<TSequence>;
+	using NextUniqueSequence = typename TUniqueTypeSequenceImpl<NextSequence>::Type;
+	using Type = TConditional<!CExistentType<FrontType, NextSequence>, TPush<FrontType, NextUniqueSequence>, NextUniqueSequence>;
+};
+
+template <>
+struct TUniqueTypeSequenceImpl<TTypeSequence<>>
+{
+	using Type = TTypeSequence<>;
+};
+
+NAMESPACE_PRIVATE_END
+
+template <CTTypeSequence TSequence>
+using TUniqueTypeSequence = typename NAMESPACE_PRIVATE::TUniqueTypeSequenceImpl<TSequence>::Type;
+
+NAMESPACE_PRIVATE_BEGIN
+
+template <typename T>
+struct TOverload
+{
+	using F = T(*)(T);
+	operator F() const { return nullptr; }
+};
+
+template <typename TSequence>
+struct TOverloadSetImpl;
+
+template <typename... Ts>
+struct TOverloadSetImpl<TTypeSequence<Ts...>> : public TOverload<Ts>... { };
+
+template <typename TSequence>
+struct TOverloadSet : public TOverloadSetImpl<TUniqueTypeSequence<TSequence>> { };
+
+NAMESPACE_PRIVATE_END
+
+template <typename T, typename TSequence>
+using TOverloadResolution = decltype(DeclVal<NAMESPACE_PRIVATE::TOverloadSet<TSequence>>()(DeclVal<T>()));
+
+NAMESPACE_END(Meta)
+
+NAMESPACE_MODULE_END(Utility)
+NAMESPACE_MODULE_END(Redcraft)
+NAMESPACE_REDCRAFT_END
diff --git a/Redcraft.Utility/Source/Public/Templates/Templates.h b/Redcraft.Utility/Source/Public/Templates/Templates.h
index b03fec6..db3a7d6 100644
--- a/Redcraft.Utility/Source/Public/Templates/Templates.h
+++ b/Redcraft.Utility/Source/Public/Templates/Templates.h
@@ -9,7 +9,7 @@
 #include "Templates/Optional.h"
 #include "Templates/Variant.h"
 #include "Templates/Any.h"
-#include "Templates/IntegerSequence.h"
+#include "Templates/Meta.h"
 #include "Templates/Tuple.h"
 #include "Templates/TypeHash.h"
 #include "Templates/Function.h"
diff --git a/Redcraft.Utility/Source/Public/Templates/Tuple.h b/Redcraft.Utility/Source/Public/Templates/Tuple.h
index ddab60b..a2bd017 100644
--- a/Redcraft.Utility/Source/Public/Templates/Tuple.h
+++ b/Redcraft.Utility/Source/Public/Templates/Tuple.h
@@ -1,11 +1,11 @@
 #pragma once
 
 #include "CoreTypes.h"
+#include "Templates/Meta.h"
 #include "Templates/Invoke.h"
 #include "Templates/Utility.h"
 #include "Templates/TypeHash.h"
 #include "TypeTraits/TypeTraits.h"
-#include "Templates/IntegerSequence.h"
 #include "Templates/ReferenceWrapper.h"
 
 #include <tuple>
@@ -21,7 +21,7 @@ class TTuple;
 
 NAMESPACE_PRIVATE_BEGIN
 
-template <typename    T    > struct TIsTTuple                   : FFalse { };
+template <typename    T > struct TIsTTuple                : FFalse { };
 template <typename... Ts> struct TIsTTuple<TTuple<Ts...>> : FTrue  { };
 
 struct FForwardingConstructor { explicit FForwardingConstructor() = default; };
@@ -34,72 +34,23 @@ template <typename TupleType>
 struct TTupleArityImpl;
 
 template <typename... Ts>
-struct TTupleArityImpl<TTuple<Ts...>> : TConstant<size_t, sizeof...(Ts)> { };
-
-template <typename... Ts>
-struct TTupleArityImpl<const TTuple<Ts...>> : TConstant<size_t, sizeof...(Ts)> { };
-
-template <typename... Ts>
-struct TTupleArityImpl<volatile TTuple<Ts...>> : TConstant<size_t, sizeof...(Ts)> { };
-
-template <typename... Ts>
-struct TTupleArityImpl<const volatile TTuple<Ts...>> : TConstant<size_t, sizeof...(Ts)> { };
+struct TTupleArityImpl<TTuple<Ts...>> : TConstant<size_t, Meta::TSize<TTypeSequence<Ts...>>> { };
 
 template <typename T, typename TupleType>
 struct TTupleIndexImpl;
 
-template <typename T, typename U, typename... Ts>
-struct TTupleIndexImpl<T, TTuple<U, Ts...>> : TConstant<size_t, TTupleIndexImpl<T, TTuple<Ts...>>::Value + 1>
-{
-	static_assert(sizeof...(Ts) != 0, "Non-existent types in tuple");
-};
-
 template <typename T, typename... Ts>
-struct TTupleIndexImpl<T, TTuple<T, Ts...>> : TConstant<size_t, 0>
-{
-	static_assert((true && ... && !CSameAs<T, Ts>), "Duplicate type in tuple");
-};
-
-template <typename T>
-struct TTupleIndexImpl<T, TTuple<>> : TConstant<size_t, INDEX_NONE> { };
-
-template <typename T, typename... Ts>
-struct TTupleIndexImpl<T, const TTuple<Ts...>> : TTupleIndexImpl<T, TTuple<Ts...>> { };
-
-template <typename T, typename... Ts>
-struct TTupleIndexImpl<T, volatile TTuple<Ts...>> : TTupleIndexImpl<T, TTuple<Ts...>> { };
-
-template <typename T, typename... Ts>
-struct TTupleIndexImpl<T, const volatile TTuple<Ts...>> : TTupleIndexImpl<T, TTuple<Ts...>> { };
+struct TTupleIndexImpl<T, TTuple<Ts...>> : TConstant<size_t, Meta::TIndex<T, TTypeSequence<Ts...>>> { };
 
 template <size_t I, typename TupleType>
 struct TTupleElementImpl;
 
-template <size_t I, typename T, typename... Ts>
-struct TTupleElementImpl<I, TTuple<T, Ts...>>
+template <size_t I, typename... Ts>
+struct TTupleElementImpl<I, TTuple<Ts...>>
 {
-	static_assert(I < sizeof...(Ts) + 1, "Invalid index in tuple");
-	using Type = TTupleElementImpl<I - 1, TTuple<Ts...>>::Type;
+	using Type = Meta::TType<I, TTypeSequence<Ts...>>;
 };
 
-template <typename T, typename... Ts>
-struct TTupleElementImpl<0, TTuple<T, Ts...>> { using Type = T; };
-
-template <size_t I, typename... Ts>
-struct TTupleElementImpl<I, TTuple<Ts...>> { };
-
-template <>
-struct TTupleElementImpl<0, TTuple<>> { };
-
-template <size_t I, typename... Ts>
-struct TTupleElementImpl<I, const TTuple<Ts...>> { using Type = TAddConst<typename TTupleElementImpl<I, TTuple<Ts...>>::Type>; };
-
-template <size_t I, typename... Ts>
-struct TTupleElementImpl<I, volatile TTuple<Ts...>> { using Type = TAddVolatile<typename TTupleElementImpl<I, TTuple<Ts...>>::Type>; };
-
-template <size_t I, typename... Ts>
-struct TTupleElementImpl<I, const volatile TTuple<Ts...>> { using Type = TAddCV<typename TTupleElementImpl<I, TTuple<Ts...>>::Type>; };
-
 template <bool bTrue, typename... Ts>
 struct TTupleConvertCopy : FTrue { };
 
@@ -247,8 +198,8 @@ public:
 	template <typename LHSTupleType, typename RHSTupleType>
 	static constexpr void Assign(LHSTupleType& LHS, RHSTupleType&& RHS)
 	{
-		static_assert(sizeof...(Indices) == TTupleArityImpl<TRemoveReference<LHSTupleType>>::Value
-			&& TTupleArityImpl<TRemoveReference<LHSTupleType>>::Value == TTupleArityImpl<TRemoveReference<RHSTupleType>>::Value,
+		static_assert(sizeof...(Indices) == TTupleArityImpl<TRemoveCVRef<LHSTupleType>>::Value
+			&& TTupleArityImpl<TRemoveCVRef<LHSTupleType>>::Value == TTupleArityImpl<TRemoveCVRef<RHSTupleType>>::Value,
 			"Cannot assign tuple from different size");
 		
 		((LHS.template GetValue<Indices>() = Forward<RHSTupleType>(RHS).template GetValue<Indices>()), ...);
@@ -292,13 +243,13 @@ template <typename T>
 concept CTTuple = NAMESPACE_PRIVATE::TIsTTuple<TRemoveCV<T>>::Value;
 
 template <CTTuple T>
-inline constexpr size_t TTupleArity = NAMESPACE_PRIVATE::TTupleArityImpl<T>::Value;
+inline constexpr size_t TTupleArity = NAMESPACE_PRIVATE::TTupleArityImpl<TRemoveCV<T>>::Value;
 
 template <typename T, CTTuple U>
-inline constexpr size_t TTupleIndex = NAMESPACE_PRIVATE::TTupleIndexImpl<T, U>::Value;
+inline constexpr size_t TTupleIndex = NAMESPACE_PRIVATE::TTupleIndexImpl<T, TRemoveCV<U>>::Value;
 
 template <size_t I, CTTuple U>
-using TTupleElement = typename NAMESPACE_PRIVATE::TTupleElementImpl<I, U>::Type;
+using TTupleElement = TCopyCV<U, typename NAMESPACE_PRIVATE::TTupleElementImpl<I, TRemoveCV<U>>::Type>;
 
 template <typename... Ts>
 class TTuple : public NAMESPACE_PRIVATE::TTupleImpl<TIndexSequenceFor<Ts...>, Ts...>
diff --git a/Redcraft.Utility/Source/Public/Templates/Utility.h b/Redcraft.Utility/Source/Public/Templates/Utility.h
index 4f9571a..2cabd3e 100644
--- a/Redcraft.Utility/Source/Public/Templates/Utility.h
+++ b/Redcraft.Utility/Source/Public/Templates/Utility.h
@@ -117,6 +117,23 @@ inline constexpr FIgnore Ignore;
 		                                           \
 	}
 
+// TOverloaded Usage Example
+// 
+//	Visit(TOverloaded {
+//		[](auto A)           { ... },
+//		[](double A)         { ... },
+//		[](const FString& A) { ... },
+//	}, Target);
+//
+template <typename... Ts>
+struct TOverloaded : Ts...
+{
+	using Ts::operator()...;
+};
+
+template <typename... Ts>
+TOverloaded(Ts...) -> TOverloaded<Ts...>;
+
 NAMESPACE_MODULE_END(Utility)
 NAMESPACE_MODULE_END(Redcraft)
 NAMESPACE_REDCRAFT_END
diff --git a/Redcraft.Utility/Source/Public/Templates/Variant.h b/Redcraft.Utility/Source/Public/Templates/Variant.h
index fcb9f83..0ef5a95 100644
--- a/Redcraft.Utility/Source/Public/Templates/Variant.h
+++ b/Redcraft.Utility/Source/Public/Templates/Variant.h
@@ -5,6 +5,7 @@
 #include "Templates/Utility.h"
 #include "Templates/TypeHash.h"
 #include "TypeTraits/TypeTraits.h"
+#include "Templates/Meta.h"
 #include "Memory/MemoryOperator.h"
 #include "Miscellaneous/Compare.h"
 #include "Miscellaneous/AssertionMacros.h"
@@ -21,86 +22,27 @@ NAMESPACE_PRIVATE_BEGIN
 template <typename    T > struct TIsTVariant                  : FFalse { };
 template <typename... Ts> struct TIsTVariant<TVariant<Ts...>> : FTrue  { };
 
-// This class is to avoid conflicting with sizeof...(Ts) > 0 constraints when using TVariant<> in tool templates
-template <typename... Ts>
-struct TVariantProxy { };
-
-template <typename TupleType>
+template <typename VariantType>
 struct TVariantNumImpl;
 
 template <typename... Ts>
-struct TVariantNumImpl<TVariant<Ts...>> : TConstant<size_t, sizeof...(Ts)> { };
+struct TVariantNumImpl<TVariant<Ts...>> : TConstant<size_t, Meta::TSize<TTypeSequence<Ts...>>> { };
 
-template <typename... Ts>
-struct TVariantNumImpl<const TVariant<Ts...>> : TConstant<size_t, sizeof...(Ts)> { };
-
-template <typename... Ts>
-struct TVariantNumImpl<volatile TVariant<Ts...>> : TConstant<size_t, sizeof...(Ts)> { };
-
-template <typename... Ts>
-struct TVariantNumImpl<const volatile TVariant<Ts...>> : TConstant<size_t, sizeof...(Ts)> { };
-
-template <typename T, typename TupleType>
+template <typename T, typename VariantType>
 struct TVariantIndexImpl;
 
-template <typename T, typename U, typename... Ts>
-struct TVariantIndexImpl<T, TVariantProxy<U, Ts...>> : TConstant<size_t, TVariantIndexImpl<T, TVariantProxy<Ts...>>::Value + 1>
-{
-	static_assert(sizeof...(Ts) != 0, "Non-existent types in variant");
-};
-
 template <typename T, typename... Ts>
-struct TVariantIndexImpl<T, TVariantProxy<T, Ts...>> : TConstant<size_t, 0>
-{
-	static_assert((true && ... && !CSameAs<T, Ts>), "Duplicate type in variant");
-};
+struct TVariantIndexImpl<T, TVariant<Ts...>> : TConstant<size_t, Meta::TIndex<T, TTypeSequence<Ts...>>> { };
 
-template <typename T>
-struct TVariantIndexImpl<T, TVariantProxy<>> : TConstant<size_t, INDEX_NONE> { };
-
-template <typename T, typename... Ts>
-struct TVariantIndexImpl<T, TVariant<Ts...>> : TVariantIndexImpl<T, TVariantProxy<Ts...>> { };
-
-template <typename T, typename... Ts>
-struct TVariantIndexImpl<T, const TVariant<Ts...>> : TVariantIndexImpl<T, TVariant<Ts...>> { };
-
-template <typename T, typename... Ts>
-struct TVariantIndexImpl<T, volatile TVariant<Ts...>> : TVariantIndexImpl<T, TVariant<Ts...>> { };
-
-template <typename T, typename... Ts>
-struct TVariantIndexImpl<T, const volatile TVariant<Ts...>> : TVariantIndexImpl<T, TVariant<Ts...>> { };
-
-template <size_t I, typename TupleType>
+template <size_t I, typename VariantType>
 struct TVariantAlternativeImpl;
 
-template <size_t I, typename T, typename... Ts>
-struct TVariantAlternativeImpl<I, TVariantProxy<T, Ts...>>
+template <size_t I, typename... Ts>
+struct TVariantAlternativeImpl<I, TVariant<Ts...>>
 {
-	static_assert(I < sizeof...(Ts) + 1, "Invalid index in variant");
-	using Type = TVariantAlternativeImpl<I - 1, TVariantProxy<Ts...>>::Type;
+	using Type = Meta::TType<I, TTypeSequence<Ts...>>;
 };
 
-template <typename T, typename... Ts>
-struct TVariantAlternativeImpl<0, TVariantProxy<T, Ts...>> { using Type = T; };
-
-template <size_t I, typename... Ts>
-struct TVariantAlternativeImpl<I, TVariantProxy<Ts...>> { };
-
-template <>
-struct TVariantAlternativeImpl<0, TVariantProxy<>> { };
-
-template <size_t I, typename... Ts>
-struct TVariantAlternativeImpl<I, TVariant<Ts...>> : TVariantAlternativeImpl<I, TVariantProxy<Ts...>> { };
-
-template <size_t I, typename... Ts>
-struct TVariantAlternativeImpl<I, const TVariant<Ts...>> { using Type = TAddConst<typename TVariantAlternativeImpl<I, TVariant<Ts...>>::Type>; };
-
-template <size_t I, typename... Ts>
-struct TVariantAlternativeImpl<I, volatile TVariant<Ts...>> { using Type = TAddVolatile<typename TVariantAlternativeImpl<I, TVariant<Ts...>>::Type>; };
-
-template <size_t I, typename... Ts>
-struct TVariantAlternativeImpl<I, const volatile TVariant<Ts...>> { using Type = TAddCV<typename TVariantAlternativeImpl<I, TVariant<Ts...>>::Type>; };
-
 template <typename T, typename... Ts>
 struct TVariantSelectedType;
 
@@ -140,13 +82,13 @@ template <typename T>
 concept CTVariant = NAMESPACE_PRIVATE::TIsTVariant<TRemoveCV<T>>::Value;
 
 template <CTVariant T>
-inline constexpr size_t TVariantNum = NAMESPACE_PRIVATE::TVariantNumImpl<T>::Value;
+inline constexpr size_t TVariantNum = NAMESPACE_PRIVATE::TVariantNumImpl<TRemoveCV<T>>::Value;
 
 template <typename T, CTVariant U>
-inline constexpr size_t TVariantIndex = NAMESPACE_PRIVATE::TVariantIndexImpl<T, U>::Value;
+inline constexpr size_t TVariantIndex = NAMESPACE_PRIVATE::TVariantIndexImpl<T, TRemoveCV<U>>::Value;
 
 template <size_t I, CTVariant U>
-using TVariantAlternative = typename NAMESPACE_PRIVATE::TVariantAlternativeImpl<I, U>::Type;
+using TVariantAlternative = TCopyCV<U, typename NAMESPACE_PRIVATE::TVariantAlternativeImpl<I, TRemoveCV<U>>::Type>;
 
 template <typename... Ts> requires (sizeof...(Ts) > 0 && (true && ... && CDestructible<Ts>))
 class TVariant
diff --git a/Redcraft.Utility/Source/Public/TypeTraits/Common.h b/Redcraft.Utility/Source/Public/TypeTraits/Common.h
index 7ab2502..4cee50a 100644
--- a/Redcraft.Utility/Source/Public/TypeTraits/Common.h
+++ b/Redcraft.Utility/Source/Public/TypeTraits/Common.h
@@ -16,7 +16,7 @@ NAMESPACE_MODULE_BEGIN(Utility)
 template <typename T, typename U> struct TBasicCommonType { };
 
 // The class template is a customization point that allows users to influence the result of TCommonReference for user
-template <typename T, typename U, template<typename> typename TQualifiers, template<typename> typename UQualifiers> struct TBasicCommonReference { };
+template <typename T, typename U, template <typename> typename TQualifiers, template <typename> typename UQualifiers> struct TBasicCommonReference { };
 
 NAMESPACE_PRIVATE_BEGIN