93 lines
2.4 KiB
C++
93 lines
2.4 KiB
C++
/*!
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* \file selection.h
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* \brief Template meta-programming type selections.
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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_selection_h__
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#define __utl_meta_selection_h__
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#include <utl/core/impl.h>
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#include <utl/meta/integral.h>
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#include <utl/meta/sfinae.h>
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/*!
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* \ingroup meta
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* \defgroup type selection
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* Type selection 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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/*!
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* Type selection
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*/
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//! @{
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//! if_, if_c
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//! @{
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namespace detail {
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template <bool If, typename...>
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struct if_c_ {
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using type = nil_; //!< avoid ill formed result
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};
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template<typename Then>
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struct if_c_<true, Then> {
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using type = Then;
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};
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template<typename Then, typename Else>
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struct if_c_<true, Then, Else> {
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using type = Then;
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};
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template<typename Then, typename Else>
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struct if_c_<false, Then, Else> {
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using type = Else;
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};
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}
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//! Select one type or another depending on a compile-time Boolean.
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template <bool B, typename... Args>
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using if_c = type_<detail::if_c_<B, Args...>>;
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//! Select one type or another depending on a compile-time Boolean type
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template <typename If, typename... Args>
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using if_ = if_c<If::type::value, Args...>;
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//! @}
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/*!
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* Named type selectors
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*/
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//! @{
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//! Select the first type of a type sequence
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template <typename T1, typename ...>
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struct first_of {
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using type = T1;
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};
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//! Select the second type of a type sequence
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template <typename T1, typename T2, typename ...>
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struct second_of {
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using type = T2;
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};
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//! @}
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}}
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//! @}
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#endif /* __utl_meta_selection_h__ */
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