1 #pragma once
2 
3 #include <mbgl/util/type_list.hpp>
4 #include <mbgl/util/tuple.hpp>
5 
6 #include <type_traits>
7 
8 namespace mbgl {
9 
10 template <class T, class... Ts>
11 struct TypeIndex;
12 
13 template <class T, class... Ts>
14 struct TypeIndex<T, T, Ts...> : std::integral_constant<std::size_t, 0> {};
15 
16 template <class T, class U, class... Ts>
17 struct TypeIndex<T, U, Ts...> : std::integral_constant<std::size_t, 1 + TypeIndex<T, Ts...>::value> {};
18 
19 template <class...> class IndexedTuple;
20 
21 // A tuple of Ts, where individual members can be accessed via `t.get<I>()` for I ∈ Is.
22 //
23 // See https://github.com/mapbox/cpp/blob/master/C%2B%2B%20Structural%20Metaprogramming.md
24 // for motivation.
25 //
26 template <class... Is, class... Ts>
27 class IndexedTuple<TypeList<Is...>, TypeList<Ts...>> : public tuple_polyfill<Ts...> {
28 public:
29     static_assert(sizeof...(Is) == sizeof...(Ts), "IndexedTuple size mismatch");
30 
31     using tuple_polyfill<Ts...>::tuple;
32 
33     template <class I>
get()34     auto& get() {
35         return get_polyfill<TypeIndex<I, Is...>::value>(*this);
36     }
37 
38     template <class I>
get() const39     const auto& get() const {
40         return get_polyfill<TypeIndex<I, Is...>::value>(*this);
41     }
42 
43     template <class... Js, class... Us>
44     IndexedTuple<TypeList<Is..., Js...>, TypeList<Ts..., Us...>>
concat(const IndexedTuple<TypeList<Js...>,TypeList<Us...>> & other) const45     concat(const IndexedTuple<TypeList<Js...>, TypeList<Us...>>& other) const {
46         return IndexedTuple<TypeList<Is..., Js...>, TypeList<Ts..., Us...>> {
47             get<Is>()...,
48             other.template get<Js>()...
49         };
50     }
51 };
52 
53 } // namespace mbgl
54