ceph/src/jaegertracing/opentelemetry-cpp/api/include/opentelemetry/nostd/detail/type_pack_element.h

   1 #pragma once
   2
   3 #include <cstddef>
   4 #include <type_traits>
   5
   6 #include "opentelemetry/nostd/utility.h"
   7 #include "opentelemetry/version.h"
   8
   9 OPENTELEMETRY_BEGIN_NAMESPACE
  10 namespace nostd
  11 {
  12 namespace detail
  13 {
  14 template <std::size_t N>
  15 using size_constant = std::integral_constant<std::size_t, N>;
  16
  17 template <std::size_t I, typename T>
  18 struct indexed_type : size_constant<I>
  19 {
  20   using type = T;
  21 };
  22
  23 template <std::size_t I, typename... Ts>
  24 struct type_pack_element_impl
  25 {
  26 private:
  27   template <typename>
  28   struct set;
  29
  30   template <std::size_t... Is>
  31   struct set<index_sequence<Is...>> : indexed_type<Is, Ts>...
  32   {};
  33
  34   template <typename T>
  35   inline static std::enable_if<true, T> impl(indexed_type<I, T>);
  36
  37   inline static std::enable_if<false> impl(...);
  38
  39 public:
  40   using type = decltype(impl(set<index_sequence_for<Ts...>>{}));
  41 };
  42
  43 template <std::size_t I, typename... Ts>
  44 using type_pack_element = typename type_pack_element_impl<I, Ts...>::type;
  45
  46 template <std::size_t I, typename... Ts>
  47 using type_pack_element_t = typename type_pack_element<I, Ts...>::type;
  48 }  // namespace detail
  49 }  // namespace nostd
  50 OPENTELEMETRY_END_NAMESPACE