|
- /*!
- * \file sfinae.h
- * \brief Template meta-programming SFINAE helpers
- *
- * 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_sfinae_h__
- #define __utl_meta_sfinae_h__
-
- #include <utl/core/impl.h>
-
- /*!
- * \ingroup meta
- * \defgroup sfinae
- * conditional use support header.
- */
- //! @{
- namespace utl {
- namespace meta {
-
- //! Tool to enable a partial specialization only if a boolean condition is true.
- //! @{
- namespace detail {
- template <typename... T>
- struct dev_null { using type = dev_null; }; //< Same as typelist
-
- template <bool If> struct when_ { };
- template <> struct when_<true> { using type = void; };
- }
- //! Well formed only if \p If is true
- template <bool If>
- using when = eval<detail::when_<If>>;
-
- //! Well formed only if all of \p Ifs are \c true
- template <bool ...Ifs>
- using when_all = detail::dev_null<
- when<Ifs>...
- >;
- //! @}
-
- //! select _Tp if \p If is true, else SFINAE
- //! We implement enable_if so we don't have to pull entire \c <type_traits> from stl
- //! @{
- template <bool If, typename _Tp = void>
- struct enable_if {
- using type = _Tp;
- };
- template<typename _Tp>
- struct enable_if <false, _Tp> { /* SFINAE*/ };
-
- //! Alias template for enable_if
- template <bool If, typename _Tp = void>
- using use_if = enable_if<If, _Tp>;
-
- //! Publicly recognized alias template for enable_if
- template<bool If, typename _Tp = void>
- using enable_if_t = eval<
- enable_if<If, _Tp>
- >;
-
- //! Uniform alias template for use_if
- template<bool If, typename _Tp = void>
- using use_if_t = eval<
- enable_if<If, _Tp>
- >;
- //! @}
-
- }}
-
- //! @}
-
- #endif /* __utl_meta_sfinae_h__ */
|