mirror of
https://github.com/bolero-MURAKAMI/Sprout.git
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89 lines
3 KiB
C++
89 lines
3 KiB
C++
/*=============================================================================
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Copyright (c) 2011-2019 Bolero MURAKAMI
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https://github.com/bolero-MURAKAMI/Sprout
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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=============================================================================*/
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#ifndef SPROUT_VARIANT_AS_VISITOR_HPP
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#define SPROUT_VARIANT_AS_VISITOR_HPP
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#include <utility>
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#include <type_traits>
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#include <sprout/config.hpp>
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#include <sprout/utility/forward.hpp>
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#include <sprout/utility/lvalue_forward.hpp>
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#include <sprout/utility/value_holder/value_holder.hpp>
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#include <sprout/type_traits/lvalue_reference.hpp>
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#include <sprout/variant/static_visitor.hpp>
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#include <sprout/functional/type_traits/has_type.hpp>
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#include <sprout/functional/type_traits/weak_result_type.hpp>
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namespace sprout {
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namespace detail {
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template<typename T, typename = void>
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struct result_type_or_void;
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template<typename T>
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struct result_type_or_void<
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T,
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typename std::enable_if<sprout::has_result_type<sprout::weak_result_type<T> >::value>::type
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> {
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public:
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typedef typename sprout::weak_result_type<T>::result_type type;
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};
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template<typename T>
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struct result_type_or_void<
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T,
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typename std::enable_if<!sprout::has_result_type<sprout::weak_result_type<T> >::value>::type
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> {
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public:
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typedef void type;
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};
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} // namespace detail
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//
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// visitor_wrapper
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//
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template<
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typename Visitor,
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typename R = typename sprout::detail::result_type_or_void<Visitor>::type
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>
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class visitor_wrapper
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: public sprout::static_visitor<R>
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{
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public:
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typedef Visitor visitor_type;
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typedef sprout::value_holder<visitor_type&> holder_type;
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private:
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holder_type v_;
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public:
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SPROUT_CONSTEXPR explicit visitor_wrapper(typename holder_type::param_type v)
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: v_(v)
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{}
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template<typename T>
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SPROUT_CONSTEXPR auto operator()(T&& t) const
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-> decltype(std::declval<holder_type const>().get()(SPROUT_FORWARD(T, t)))
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{
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return v_.get()(SPROUT_FORWARD(T, t));
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}
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};
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//
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// as_visitor
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//
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template<typename Visitor>
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inline SPROUT_CONSTEXPR sprout::visitor_wrapper<typename std::remove_reference<typename sprout::lvalue_reference<Visitor>::type>::type>
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as_visitor(Visitor&& visitor) {
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typedef sprout::visitor_wrapper<typename std::remove_reference<typename sprout::lvalue_reference<Visitor>::type>::type> type;
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return type(sprout::lvalue_forward<Visitor>(visitor));
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}
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template<typename R, typename Visitor>
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inline SPROUT_CONSTEXPR sprout::visitor_wrapper<typename std::remove_reference<typename sprout::lvalue_reference<Visitor>::type>::type, R>
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as_visitor(Visitor&& visitor) {
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typedef sprout::visitor_wrapper<typename std::remove_reference<typename sprout::lvalue_reference<Visitor>::type>::type, R> type;
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return type(sprout::lvalue_forward<Visitor>(visitor));
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}
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} // namespace sprout
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#endif // #ifndef SPROUT_VARIANT_AS_VISITOR_HPP
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