utl/include/utl/meta/sfinae.h

/*!
 * \file    use.h
 * \brief   Template meta-programming SFINAE 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_use_h__
#define __utl_meta_use_h__

#include <utl/impl/version.h>
#include <utl/meta/logical.h>


/*!
 * \ingroup meta
 * \defgroup use
 * conditional use support header. This is a SFINAE helper
 */
//! @{
namespace utl {

   //! If same type resolves to _Ret, else to SFINAE
   //! @{
   template <typename _Tp1, typename _Tp2, typename _Ret>
   struct use_if_same_ {
      using type = enable_if_t <
                      same_<_Tp1, _Tp2>::value,
                      _Ret
                   >;
   };
   template <typename _Tp1, typename _Tp2, typename _Ret>
   using use_if_same_t = typename use_if_same_<_Tp1, _Tp2, _Ret>::type;
   //! @}

   //! If same type resolves to SFINAE, else to _Ret
   //! @{
   template <typename _Tp1, typename _Tp2, typename _Ret>
   struct discard_if_same_ {
      using type = enable_if_t <
                      !same_<_Tp1, _Tp2>::value,
                      _Ret
                   >;
   };
   template <typename _Tp1, typename _Tp2, typename _Ret>
   using discard_if_same_t = typename discard_if_same_<_Tp1, _Tp2, _Ret>::type;
   //! @}

}

//! @}
#endif /* __utl_meta_use_h__ */