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◆ main openmsx / src / utils / function_ref.hh
2.0 KiB · C++ · last changed chore(): initial commit 1 month ago source blame history raw
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// This is a simplified / stripped-down version of:
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//   https://github.com/TartanLlama/function_ref/blob/master/include/tl/function_ref.hpp
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///
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// function_ref - A low-overhead non-owning function
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// Written in 2017 by Simon Brand (@TartanLlama)
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//
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// To the extent possible under law, the author(s) have dedicated all
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// copyright and related and neighboring rights to this software to the
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// public domain worldwide. This software is distributed without any warranty.
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//
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// You should have received a copy of the CC0 Public Domain Dedication
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// along with this software. If not, see
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// <http://creativecommons.org/publicdomain/zero/1.0/>.
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///
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#ifndef FUNCTION_REF_HH
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#define FUNCTION_REF_HH
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#include <functional>
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#include <type_traits>
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#include <utility>
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template<typename F> class function_ref;
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template<typename R, typename... Args>
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class function_ref<R(Args...)>
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{
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public:
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	constexpr function_ref() noexcept = delete;
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	template<typename F,
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	         std::enable_if_t<!std::is_same_v<std::decay_t<F>, function_ref> &&
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	                          std::is_invocable_r_v<R, F &&, Args...>>* = nullptr>
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	constexpr function_ref(F&& f) noexcept
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		: obj(const_cast<void*>(static_cast<const void*>(std::addressof(f))))
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	{
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		callback = [](void* o, Args... args) -> R {
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			return std::invoke(*static_cast<std::add_pointer_t<F>>(o),
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			                   std::forward<Args>(args)...);
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		};
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	}
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	template<typename F,
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	         std::enable_if_t<std::is_invocable_r_v<R, F &&, Args...>>* = nullptr>
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	constexpr function_ref& operator=(F&& f) noexcept
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	{
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		obj = reinterpret_cast<void*>(std::addressof(f));
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		callback = [](void* o, Args... args) {
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			return std::invoke(*reinterpret_cast<std::add_pointer_t<F>>(o),
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			                   std::forward<Args>(args)...);
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		};
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		return *this;
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	}
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	constexpr R operator()(Args... args) const
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	{
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		return callback(obj, std::forward<Args>(args)...);
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	}
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private:
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	void* obj = nullptr;
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	R (*callback)(void*, Args...) = nullptr;
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};
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template<typename R, typename... Args>
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function_ref(R(*)(Args...)) -> function_ref<R(Args...)>;
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#endif