nth_type.h

/******************************************************************************
The MIT License(MIT)
 
Embedded Template Library.
https://github.com/ETLCPP/etl
https://www.etlcpp.com
 
Copyright(c) 2021 John Wellbelove
 
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#ifndef ETL_NTH_TYPE_INCLUDED
#define ETL_NTH_TYPE_INCLUDED
 
#include "platform.h"
#include "static_assert.h"
#include "type_list.h"
 
#if ETL_USING_CPP11
namespace etl
{
  namespace private_nth_type
  {
    //***********************************
    template <size_t Index, typename T1, typename... TRest>
    struct nth_type_helper
    {
      using type = typename nth_type_helper<Index - 1U, TRest...>::type;
    };
 
    template <typename T1, typename... TRest>
    struct nth_type_helper<0U, T1, TRest...>
    {
      using type = T1;
    };
  } // namespace private_nth_type
 
  //***********************************
  template <size_t Index, typename... TTypes>
  struct nth_type
  {
    ETL_STATIC_ASSERT(Index < sizeof...(TTypes), "etl::nth_type index 'Index' out of bounds");
 
    using type      = typename private_nth_type::nth_type_helper<Index, TTypes...>::type;
    using type_list = etl::type_list<TTypes...>;
  };
 
  //***********************************
  template <size_t Index, typename... TTypes>
  struct nth_type<Index, etl::type_list<TTypes...>>
  {
    using type      = typename nth_type<Index, TTypes...>::type;
    using type_list = typename nth_type<Index, TTypes...>::type_list;
  };
 
  //***********************************
  template <size_t Index, typename... TTypes>
  using nth_type_t = typename nth_type<Index, TTypes...>::type;
} // namespace etl
#endif
#endif