Util: Add a y-combinator template class
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/*
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* This file is part of OpenTTD.
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* OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
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* OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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* See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
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*/
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/** @file y_combinator.hpp Y-combinator template implementation to support recursive lambdas and similar. */
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#ifndef Y_COMBINATOR_HPP
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#define Y_COMBINATOR_HPP
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#include <functional>
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#include <utility>
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/* Based on C++ std library proposal: https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0200r0.html */
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template<class F>
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class y_combinator_result {
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F func_;
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public:
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template<class T>
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explicit y_combinator_result(T &&func): func_(std::forward<T>(func)) {}
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template<class ...Args>
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decltype(auto) operator()(Args &&...args) {
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return func_(std::ref(*this), std::forward<Args>(args)...);
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}
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};
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template<class F>
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decltype(auto) y_combinator(F &&func) {
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return y_combinator_result<std::decay_t<F>>(std::forward<F>(func));
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}
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#endif /* Y_COMBINATOR_HPP */
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