1#ifndef ANDROID_PDX_RPC_ENUMERATION_H_ 2#define ANDROID_PDX_RPC_ENUMERATION_H_ 3 4#include <pdx/rpc/sequence.h> 5 6namespace android { 7namespace pdx { 8namespace rpc { 9 10// Utility for manipulating lists of types. Provides operations to lookup an 11// element by type or index. 12 13namespace detail { 14 15// Helper type that captures type and index for each element of a type 16// enumeration. 17template <std::size_t I, typename T> 18struct IndexedElement { 19 using Type = T; 20 static constexpr std::size_t Index = I; 21}; 22 23// Helper type that captures an IndexSequence and corresponding list of types. 24template <typename Is, typename... Ts> 25struct ElementIndexer; 26 27// Partial specialization that generates an instantiation of IndexElement<I, T> 28// for each element of a type enumeration using inheritance. Once a type 29// enumeration is instantiated this way the compiler is able to deduce either I 30// or T from the other using the method below. 31template <std::size_t... Is, typename... Ts> 32struct ElementIndexer<IndexSequence<Is...>, Ts...> : IndexedElement<Is, Ts>... { 33}; 34 35// Helper function that causes the compiler to deduce an IndexedElement<I, T> 36// given T. 37template <typename T, std::size_t I> 38static IndexedElement<I, T> SelectElementByType(IndexedElement<I, T>); 39 40// Helper function that causes the compiler to deduce an IndexedElement<I, T> 41// given I. 42template <std::size_t I, typename T> 43static IndexedElement<I, T> SelectElementByIndex(IndexedElement<I, T>); 44 45} // namespace detail 46 47// Deduces the IndexedElement<I, T> given T and a type sequence Ts. This may be 48// used to determine the index of T within Ts at compile time. 49template <typename T, typename... Ts> 50using ElementForType = decltype(detail::SelectElementByType<T>( 51 detail::ElementIndexer<typename IndexSequenceFor<Ts...>::type, Ts...>{})); 52 53// Deduces the IndexedElement<I, T> given I and a type sequence Ts. This may be 54// used to determine the type of the element at index I within Ts at compile 55// time. Tuple operations may also be used to accomplish the same task, however 56// this implementation is provided here for symmetry. 57template <std::size_t I, typename... Ts> 58using ElementForIndex = decltype(detail::SelectElementByIndex<I>( 59 detail::ElementIndexer<typename IndexSequenceFor<Ts...>::type, Ts...>{})); 60 61} // namespace rpc 62} // namespace pdx 63} // namespace android 64 65#endif // ANDROID_PDX_RPC_ENUMERATION_H_ 66