utl/include/utl/meta/idx_sequence.h

/*!
 * \file    pack.h
 * \brief   Template meta-programming parameter pack container
 *
 * Copyright (C) 2018-2019 Christos Choutouridis
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 3
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#ifndef __utl_meta_idx_sequence_h__
#define __utl_meta_idx_sequence_h__

#include <utl/core/impl.h>
#include <utl/meta/integral.h>


/*!
 * \ingroup meta
 * \defgroup index_sequence
 */
//! @{

namespace utl {
namespace meta {

   /*!
    * Class template integer_sequence
    */
   template<typename _Tp, _Tp... _Idx>
   struct integer_sequence {
      using value_type = _Tp;
      static constexpr size_t size() noexcept {
         return sizeof...(_Idx);
      }
   };

   //! Alias template index_sequence
   template<index_t... _Idx>
   using index_sequence = integer_sequence<index_t, _Idx...>;

   //! make_integer_sequence
   //! @{
   namespace detail {
      // Stores a tuple of indices
      template<size_t... Idxs> struct index_tuple { };

      // Concatenates two index_tuples.
      template<typename It1, typename It2> struct it_cat_;

      template<size_t... It1, size_t... It2>
      struct it_cat_ <index_tuple<It1...>, index_tuple<It2...>> {
         using type = index_tuple<It1..., (It2 + sizeof...(It1))...>;
      };

      // Builds an index_tuple<0, 1, 2, ..., _Num-1>.
      template<size_t _Num>
      struct make_index_tuple_
         : it_cat_<eval<make_index_tuple_<_Num / 2>>,
                   eval<make_index_tuple_<_Num - _Num / 2>>>
      { };
      // termination specialization for 1
      template<>
      struct make_index_tuple_<1> {
         using type = index_tuple<0>;
      };
      // termination specialization for 0
      template<>
      struct make_index_tuple_<0> {
         using type = index_tuple<>;
      };

      // factory type
      template<typename _Tp, _Tp _Num,
               typename _ISeq = eval<make_index_tuple_<_Num>>>
      struct make_integer_sequence_;

      template<typename _Tp, _Tp _Num,  size_t... _Idx>
      struct make_integer_sequence_<_Tp, _Num, index_tuple<_Idx...>> {
         static_assert( _Num >= 0,
               "Cannot make integer sequence of negative length" );
          using type = integer_sequence<_Tp, static_cast<_Tp>(_Idx)...>;
      };
   }
   //! Alias template make_integer_sequence
   //! Complexity \f$ O(log N) \f$
   template<typename _Tp, _Tp N>
   using make_integer_sequence = eval<detail::make_integer_sequence_<_Tp, N>>;

   //! Alias template make_index_sequence
   //! Complexity \f$ O(log N) \f$
   template<index_t N>
   using make_index_sequence = make_integer_sequence<index_t, N>;

   //! Alias template index_sequence_for
   //! Complexity \f$ O(log N) \f$
   //!   where N is sizeof...(_Ts)
   template<typename... _Ts>
   using index_sequence_for = make_index_sequence<sizeof...(_Ts)>;
   //! @}

}}
//! @}
#endif /* __utl_meta_idx_sequence_h__ */