71 lines
2.1 KiB
C++
71 lines
2.1 KiB
C++
#pragma once
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#include <mbgl/util/type_list.hpp>
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#include <tuple>
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#include <type_traits>
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namespace mbgl {
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template <class T, class... Ts>
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struct TypeIndex;
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template <class T, class... Ts>
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struct TypeIndex<T, T, Ts...> : std::integral_constant<std::size_t, 0> {};
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template <class T, class U, class... Ts>
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struct TypeIndex<T, U, Ts...> : std::integral_constant<std::size_t, 1 + TypeIndex<T, Ts...>::value> {};
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template <class...>
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class IndexedTuple;
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/// A tuple of Ts, where individual members can be accessed via `t.get<I>()` for I ∈ Is.
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///
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/// See
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/// https://github.com/mapbox/cpp/blob/1bb519ef25edd6169f1d6d8a65414044616590a9/docs/structural-metaprogramming.md
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/// for motivation.
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template <class... Is, class... Ts>
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class IndexedTuple<TypeList<Is...>, TypeList<Ts...>> : public std::tuple<Ts...> {
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public:
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static_assert(sizeof...(Is) == sizeof...(Ts), "IndexedTuple size mismatch");
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template <class I>
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static constexpr std::size_t getIndex() {
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return TypeIndex<I, Is...>::value;
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}
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template <class I>
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constexpr auto& get() {
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return std::get<getIndex<I>()>(*this);
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}
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template <class I>
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constexpr const auto& get() const {
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return std::get<getIndex<I>()>(*this);
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}
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template <class... Us>
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constexpr IndexedTuple(Us&&... other)
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: std::tuple<Ts...>(std::forward<Us>(other)...) {}
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template <class... Js, class... Us>
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constexpr IndexedTuple<TypeList<Is..., Js...>, TypeList<Ts..., Us...>> concat(
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const IndexedTuple<TypeList<Js...>, TypeList<Us...>>& other) const {
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return IndexedTuple<TypeList<Is..., Js...>, TypeList<Ts..., Us...>>{get<Is>()..., other.template get<Js>()...};
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}
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// Help out MSVC++
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constexpr bool operator==(const IndexedTuple<TypeList<Is...>, TypeList<Ts...>>& other) const {
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return static_cast<const std::tuple<Ts...>&>(*this) == static_cast<const std::tuple<Ts...>&>(other);
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}
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constexpr bool operator!=(const IndexedTuple<TypeList<Is...>, TypeList<Ts...>>& other) const {
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return !(*this == other);
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}
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};
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template <class, class T>
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using ExpandToType = T;
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} // namespace mbgl
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