Type enumerator

type_enumerator.hpp

/*
 * Copyright (C) 2014 LAN Xingcan
 * All right reserved
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */


#ifndef LANXC_TYPE_NUMBERATOR_HPP_INCLUDED
#define LANXC_TYPE_NUMBERATOR_HPP_INCLUDED
#include <type_traits>


namespace lanxc
{

  template<typename ...Types>
  struct type_enumerator;

  template<>
  struct type_enumerator<>
  {
    template<typename>
    struct unique_checker {};

    template<typename Type, typename ...Types>
    struct value_evaluator;

    template<unsigned Value, typename ...Types>
    struct type_evaluator;

  };


  template<typename Type, typename ...Remains>
  struct type_enumerator<>::value_evaluator<Type, Type, Remains...>
  {
    static constexpr unsigned value = 1;
  };

  template<typename Type, typename First, typename ...Remains>
  struct type_enumerator<>::value_evaluator<Type, First, Remains...>
  {
    static_assert(sizeof...(Remains) > 0, "Type not in type list");
    static constexpr unsigned value = 1 + type_enumerator<>::value_evaluator<Type, Remains...>::value;
  };

  template<typename First, typename ...Types>
  struct type_enumerator<>::type_evaluator<1, First, Types...>
  {
    using type = First;
  };

  template<unsigned Value, typename First, typename ...Types>
  struct type_enumerator<>::type_evaluator<Value, First, Types...>
  {
    static_assert(Value <= sizeof...(Types) + 1, "Value is greater than length of type list");
    using type = typename type_enumerator<>::type_evaluator<Value - 1, Types...>;
  };

  template<typename ...Args>
  struct type_enumerator : type_enumerator<>::unique_checker<Args>...
  {
    template<typename T>
    static constexpr typename std::enable_if<
      std::is_base_of<type_enumerator<>::unique_checker<T>, type_enumerator>::value,
      unsigned>::type
    value()
    {
      return type_enumerator<>::value_evaluator<T, Args...>::value;
    }

    template<unsigned N>
    using type = typename type_enumerator<>::type_evaluator<N, Args...>::type;
  };
}
#endif