type_select.h

/******************************************************************************
The MIT License(MIT)
 
Embedded Template Library.
https://github.com/ETLCPP/etl
https://www.etlcpp.com
 
Copyright(c) 2018 John Wellbelove
 
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of this software and associated documentation files(the "Software"), to deal
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The above copyright notice and this permission notice shall be included in all
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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******************************************************************************/
 
#ifndef ETL_TYPE_SELECT_INCLUDED
#define ETL_TYPE_SELECT_INCLUDED
 
#include "platform.h"
#include "null_type.h"
#include "static_assert.h"
#include "type_traits.h"
namespace etl
{
#if ETL_USING_CPP11 && !defined(ETL_TYPE_SELECT_FORCE_CPP03_IMPLEMENTATION)
  //***************************************************************************
  // Variadic version.
  //***************************************************************************
  template <typename... TTypes>
  struct type_select
  {
  private:
 
    //***********************************
    template <size_t Id, size_t Index, typename T1, typename... TRest>
    struct type_select_helper
    {
      using type = typename etl::conditional< Id == Index, T1, typename type_select_helper<Id, Index + 1, TRest...>::type>::type;
    };
 
    //***********************************
    template <size_t Id, size_t Index, typename T1>
    struct type_select_helper<Id, Index, T1>
    {
      using type = T1;
    };
 
  public:
 
    template <size_t Id>
    struct select
    {
      static_assert(Id < sizeof...(TTypes), "Illegal type_select::select index");
 
      using type = typename type_select_helper<Id, 0, TTypes...>::type;
    };
 
    template <size_t Id>
    using select_t = typename select<Id>::type;
  };
 
  //***************************************************************************
  // Select type alias
  //***************************************************************************
  template <size_t Index, typename... TTypes>
  using type_select_t = typename etl::type_select<TTypes...>::template select_t<Index>;
 
#else
  #include "private/type_select_cpp03.h"
#endif
} // namespace etl
 
#endif