86 lines
2.4 KiB
C++
86 lines
2.4 KiB
C++
/*!
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* \file sfinae.h
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* \brief Template meta-programming SFINAE helpers
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*
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* Copyright (C) 2018 Christos Choutouridis
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as
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* published by the Free Software Foundation, either version 3
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef __utl_meta_sfinae_h__
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#define __utl_meta_sfinae_h__
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#include <utl/core/impl.h>
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/*!
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* \ingroup meta
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* \defgroup sfinae
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* conditional use support header.
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*/
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//! @{
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namespace utl {
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namespace meta {
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//! Tool to enable a partial specialization only if a boolean condition is true.
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//! @{
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namespace detail {
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template <typename... T>
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struct dev_null { using type = dev_null; }; //< Same as typelist
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template <bool If> struct when_ { };
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template <> struct when_<true> { using type = void; };
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}
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//! Well formed only if \p If is true
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template <bool If>
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using when = type_<detail::when_<If>>;
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//! Well formed only if all of \p Ifs are \c true
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template <bool ...Ifs>
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using when_all = detail::dev_null<
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when<Ifs>...
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>;
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//! @}
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//! select _Tp if \p If is true, else SFINAE
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//! We implement eneble_if so we don't have to pull entire \c <type_traits> from stl
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//! @{
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template <bool If, typename _Tp = void>
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struct enable_if {
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using type = _Tp;
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};
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template<typename _Tp>
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struct enable_if <false, _Tp> { /* SFINAE*/ };
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//! Alias template for enable_if
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template <bool If, typename _Tp = void>
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using use_if = enable_if<If, _Tp>;
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//! Publicly recognized alias template for enable_if
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template<bool If, typename _Tp = void>
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using enable_if_t = type_<
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enable_if<If, _Tp>
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>;
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//! Uniform alias template for use_if
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template<bool If, typename _Tp = void>
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using use_if_t = type_<
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enable_if<If, _Tp>
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>;
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//! @}
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}}
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//! @}
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#endif /* __utl_meta_sfinae_h__ */
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