make TypeAt instantiate less templates

Author: BartolomeyKant

aether/meta/type_list.h

@@ -18,30 +18,72 @@
 #define AETHER_META_TYPE_LIST_H_
 
 #include <cstddef>
-#include <utility>
+#include <type_traits>
 
 namespace ae {
 template <typename... T>
-struct TypeList {
-  TypeList() = default;
+struct TypeList {};
+
+template <typename... T>
+struct TypeListMaker {
+  using type = TypeList<std::decay_t<T>...>;
+
   template <typename... U>
-  explicit constexpr TypeList(U&&...) {}
+  explicit constexpr TypeListMaker(U&&...) {}
 };
 
 template <typename... T>
-TypeList(T...) -> TypeList<T...>;
+TypeListMaker(T&&...) -> TypeListMaker<T...>;
+
+static inline constexpr std::size_t GetTypeAtChunkSize = 10;
+
+template <std::size_t I, typename T0, typename T1 = void, typename T2 = void,
+          typename T3 = void, typename T4 = void, typename T5 = void,
+          typename T6 = void, typename T7 = void, typename T8 = void,
+          typename T9 = void>
+static constexpr auto GetTypeAtChunk() {
+  static_assert(I < GetTypeAtChunkSize);
+  if constexpr (I == 0) {
+    return std::type_identity<T0>{};
+  } else if constexpr (I == 1) {
+    return std::type_identity<T1>{};
+  } else if constexpr (I == 2) {
+    return std::type_identity<T2>{};
+  } else if constexpr (I == 3) {
+    return std::type_identity<T3>{};
+  } else if constexpr (I == 4) {
+    return std::type_identity<T4>{};
+  } else if constexpr (I == 5) {
+    return std::type_identity<T5>{};
+  } else if constexpr (I == 6) {
+    return std::type_identity<T6>{};
+  } else if constexpr (I == 7) {
+    return std::type_identity<T7>{};
+  } else if constexpr (I == 8) {
+    return std::type_identity<T8>{};
+  } else if constexpr (I == 9) {
+    return std::type_identity<T9>{};
+  }
+}
+
+template <std::size_t I, typename T0, typename T1 = void, typename T2 = void,
+          typename T3 = void, typename T4 = void, typename T5 = void,
+          typename T6 = void, typename T7 = void, typename T8 = void,
+          typename T9 = void, typename... Ts>
+static constexpr auto GetTypeAt() {
+  if constexpr (I < GetTypeAtChunkSize) {
+    return GetTypeAtChunk<I, T0, T1, T2, T3, T4, T5, T6, T7, T8, T9>();
+  } else {
+    return GetTypeAt<I - GetTypeAtChunkSize, Ts...>();
+  }
+}
 
 template <std::size_t I, typename TList>
 struct TypeAt;
 
-template <std::size_t I, typename T, typename... Ts>
-struct TypeAt<I, TypeList<T, Ts...>> {
-  using type = typename TypeAt<I - 1, TypeList<Ts...>>::type;
-};
-
-template <typename T, typename... Ts>
-struct TypeAt<0, TypeList<T, Ts...>> {
-  using type = T;
+template <std::size_t I, typename... Ts>
+struct TypeAt<I, TypeList<Ts...>> {
+  using type = typename decltype(GetTypeAt<I, Ts...>())::type;
 };
 
 template <std::size_t I, typename TList>

aether/reflect/reflect_impl.h

@@ -248,9 +248,10 @@ struct IsReflectable<T,
   constexpr auto FieldList() const {                                          \
     using SelfType = std::decay_t<decltype(*this)>;                           \
     static_assert(sizeof(SelfType) != 0);                                     \
-    constexpr auto fields = ::ae::TypeList{__VA_ARGS__};                      \
+    auto fields = ::ae::TypeListMaker{__VA_ARGS__};                           \
     using TypeFieldTypeList =                                                 \
-        ::ae::JoinedTypeList_t<::ae::TypeList<SelfType>, decltype(fields)>;   \
+        ::ae::JoinedTypeList_t<::ae::TypeList<SelfType>,                      \
+                               typename decltype(fields)::type>;              \
     using FL = typename ::ae::TypeListToTemplate<                             \
         ::ae::reflect::reflect_internal::FieldList, TypeFieldTypeList>::type; \
     return FL{};                                                              \
@@ -264,10 +265,10 @@ struct IsReflectable<T,
   constexpr auto FieldList() const {                                          \
     using SelfType = std::decay_t<decltype(*this)>;                           \
     static_assert(sizeof(SelfType) != 0);                                     \
-    constexpr auto fields =                                                   \
-        ::ae::TypeList{_AE_APPLY_MACRO(AE_MMBR, __VA_ARGS__)};                \
+    auto fields = ::ae::TypeListMaker{_AE_APPLY_MACRO(AE_MMBR, __VA_ARGS__)}; \
     using TypeFieldTypeList =                                                 \
-        ::ae::JoinedTypeList_t<::ae::TypeList<SelfType>, decltype(fields)>;   \
+        ::ae::JoinedTypeList_t<::ae::TypeList<SelfType>,                      \
+                               typename decltype(fields)::type>;              \
     using FL = typename ::ae::TypeListToTemplate<                             \
         ::ae::reflect::reflect_internal::FieldList, TypeFieldTypeList>::type; \
     return FL{};                                                              \

tests/test-meta/test-type-list.cpp

@@ -112,6 +112,7 @@ void TestNTypesReverse() {
 void test_Ntypes() {
   RUN_TEST(TestNTypes<1>);
   RUN_TEST(TestNTypes<10>);
+
   RUN_TEST(TestNTypes<100>);
   RUN_TEST(TestNTypes<450>);