79 lines
2.3 KiB
C++
79 lines
2.3 KiB
C++
/* === This file is part of Calamares - <https://calamares.io> ===
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*
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* SPDX-FileCopyrightText: 2020 Adriaan de Groot <groot@kde.org>
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* SPDX-License-Identifier: GPL-3.0-or-later
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*
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* Calamares is Free Software: see the License-Identifier above.
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*
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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 >
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struct sfinae_true : std::true_type
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{
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};
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} // namespace Traits
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} // namespace CalamaresUtils
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#define DECLARE_HAS_METHOD( m ) \
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namespace CalamaresUtils \
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{ \
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namespace Traits \
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{ \
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struct has_##m \
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{ \
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template < class T > \
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static auto f( int ) -> sfinae_true< decltype( &T::m ) >; \
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template < class T > \
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static auto f( long ) -> std::false_type; \
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template < class T > \
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using t = decltype( f< T >( 0 ) ); \
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}; \
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} \
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} \
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template < class T > \
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using has_##m = CalamaresUtils::Traits::has_##m ::t< T >;
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#endif
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