[core] Add support for data-driven styling

1 files changed, 11 insertions, 2 deletions

diff --git a/src/mbgl/util/indexed_tuple.hpp b/src/mbgl/util/indexed_tuple.hpp
index 110e7dce12..a414639530 100644
--- a/src/mbgl/util/indexed_tuple.hpp
+++ b/src/mbgl/util/indexed_tuple.hpp
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <mbgl/util/type_list.hpp>
+
 #include <type_traits>
 #include <tuple>
 
@@ -14,8 +16,6 @@ struct TypeIndex<T, T, Ts...> : std::integral_constant<std::size_t, 0> {};
 template <class T, class U, class... Ts>
 struct TypeIndex<T, U, Ts...> : std::integral_constant<std::size_t, 1 + TypeIndex<T, Ts...>::value> {};
 
-template <class...> class TypeList {};
-
 template <class...> class IndexedTuple;
 
 // A tuple of Ts, where individual members can be accessed via `t.get<I>()` for I ∈ Is.
@@ -42,6 +42,15 @@ public:
     const auto& get() const {
         return std::get<Index<I>>(*this);
     }
+
+    template <class... Js, class... Us>
+    IndexedTuple<TypeList<Is..., Js...>, TypeList<Ts..., Us...>>
+    concat(const IndexedTuple<TypeList<Js...>, TypeList<Us...>>& other) const {
+        return IndexedTuple<TypeList<Is..., Js...>, TypeList<Ts..., Us...>> {
+            get<Is>()...,
+            other.template get<Js>()...
+        };
+    }
 };
 
 } // namespace mbgl