[core] introduce TypeListConcat and TypeList::ExpandInto

1 files changed, 26 insertions, 2 deletions

diff --git a/include/mbgl/util/type_list.hpp b/include/mbgl/util/type_list.hpp
index 4a5e95c8a4..1b594bf7f6 100644
--- a/include/mbgl/util/type_list.hpp
+++ b/include/mbgl/util/type_list.hpp
@@ -5,8 +5,11 @@
 
 namespace mbgl {
 
-template <class...>
-class TypeList {};
+template <class... Ts>
+struct TypeList {
+    template <template <class...> class T, class... Ps>
+    using ExpandInto = T<Ps..., Ts...>;
+};
 
 namespace detail {
 
@@ -32,9 +35,30 @@ struct TypeFilter<TypeList<T, Ts...>, Predicate> {
     using Type = std::conditional_t<Predicate<T>::value, typename TypeCons<T, Tail>::Type, Tail>;
 };
 
+template <class...>
+struct TypeListConcat;
+
+template <>
+struct TypeListConcat<> {
+    using Type = TypeList<>;
+};
+
+template <class... As>
+struct TypeListConcat<TypeList<As...>> {
+    using Type = TypeList<As...>;
+};
+
+template <class... As, class... Bs, class... Rs>
+struct TypeListConcat<TypeList<As...>, TypeList<Bs...>, Rs...> {
+    using Type = typename TypeListConcat<TypeList<As..., Bs...>, Rs...>::Type;
+};
+
 } // namespace detail
 
 template <class TypeList, template <class> class Predicate>
 using FilteredTypeList = typename detail::TypeFilter<TypeList, Predicate>::Type;
 
+template <class... Ts>
+using TypeListConcat = typename detail::TypeListConcat<Ts...>::Type;
+
 } // namespace mbgl