78 lines
2.8 KiB
C
78 lines
2.8 KiB
C
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/* === This file is part of Calamares - <https://github.com/calamares> ===
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*
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* SPDX-FileCopyrightText: 2020 Adriaan de Groot <groot@kde.org>
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*
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* Calamares is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Calamares 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 General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Calamares. If not, see <http://www.gnu.org/licenses/>.
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*
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* SPDX-License-Identifier: GPL-3.0-or-later
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* License-Filename: LICENSE
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*
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*/
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#ifndef UTILS_TRAITS_H
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#define UTILS_TRAITS_H
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#include <type_traits>
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namespace CalamaresUtils
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{
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/** @brief Traits machinery lives in this namespace
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*
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* The primary purpose of this namespace is to hold machinery that
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* is created by the DECLARE_HAS_METHOD macro.
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*
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* The DECLARE_HAS_METHOD macro builds machinery to check whether
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* a class has a particular named method. This can be used to
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* specialize templates elsewhere for use with classes with, or without,
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* the named method.
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*
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* To use the machinery (which is not that sophisticated):
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*
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* - Put `DECLARE_HAS_METHOD(myFunction)` somewhere in file scope.
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* This puts together the machinery for detecting if `myFunction`
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* is a method of some class.
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* - At global scope, `has_myFunction<T>` is now either std::true_type,
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* if the type `T` has a method `T::myFunction`, or std::false_type,
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* if it does not.
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*
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* To specialize template methods based on the presence of the named
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* method, write **three** overloads:
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*
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* - `template<class T> myMethod(args ..., const std::true_type& )`
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* This is the implementation where class T has `myFunction`.
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* - `template<class T> myMethod(args ..., const std::false_type& )`
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* This is the implementation without.
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* - `template<class T> myMethod(args ...)` is the general implementation,
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* which can call the specialized implementations with
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* `return myMethod(args ..., has_myFunction<T>{})`
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*/
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namespace Traits
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{
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template< class > struct sfinae_true : std::true_type{};
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}
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}
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#define DECLARE_HAS_METHOD(m) \
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namespace CalamaresUtils { namespace Traits { \
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struct has_ ## m { \
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template< class T > static auto f(int) -> sfinae_true<decltype(&T:: m)>; \
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template< class T > static auto f(long) -> std::false_type; \
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template< class T > using t = decltype( f <T>(0) ); \
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}; } } \
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template< class T > using has_ ## m = CalamaresUtils::Traits:: has_ ## m ::t<T>;
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#endif
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