utl/include/utl/meta/void_t.h

/*!
 * \file    void_t.h
 * \brief   Template meta-programming helpers
 *
 * Copyright (C) 2018 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_void_t_h__
#define __utl_meta_void_t_h__

#include <utl/impl/version.h>

//! \ingroup meta
//! \defgroup void_t
//! A void_t implementation for utl
//! @{
namespace utl {

   /*!
    * Utility meta-function that maps a sequence of any types to the type void
    * \note The idea is:
    *    template <typename ...>
    *    using void_t = void;
    *
    * Until CWG 1558 (a C++14 defect), unused parameters in alias templates were not
    * guaranteed to ensure SFINAE and could be ignored, so earlier compilers require
    * a more complex definition of void_t, such as the following implementation
    * https://en.cppreference.com
    */
   template<typename... _Ts>
   struct void_impl {
      typedef void type;
   };
   //! The actual void_t type alias
   template<typename... _Ts>
   using void_t = typename void_impl<_Ts...>::type;
}
//! @}

#endif /* __utl_meta_void_t_h__ */