90 lines
2.4 KiB
C++
90 lines
2.4 KiB
C++
/*
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This file is part of Telegram Desktop,
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the official desktop application for the Telegram messaging service.
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For license and copyright information please follow this link:
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https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
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*/
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#pragma once
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namespace base {
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namespace details {
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// This implementation was taken from range-v3 library.
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// It was modified so that more than one of passed function objects
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// could be called with an argument list and the first one that
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// matches gets used instead of a compile-time ambiguity error.
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//
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// This allows to write "default" visitor handlers with [](auto&&) syntax.
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template <typename ...Args>
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constexpr bool is_callable_v = rpl::details::is_callable_plain_v<Args...>;
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template <typename ...Args>
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struct overloaded;
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template <>
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struct overloaded<> {
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};
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template <typename First, typename ...Rest>
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struct overloaded<First, Rest...>
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: private First
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, private overloaded<Rest...> {
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private:
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using Others = overloaded<Rest...>;
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public:
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overloaded() = default;
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constexpr overloaded(First first, Rest... rest)
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: First(std::move(first))
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, Others(std::move(rest)...) {
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}
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template <typename... Args>
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auto operator()(Args&&... args)
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-> decltype(std::declval<First&>()(std::forward<Args>(args)...)) {
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return static_cast<First&>(*this)(std::forward<Args>(args)...);
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}
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template <typename... Args>
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auto operator()(Args&&... args) const
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-> decltype(std::declval<const First&>()(std::forward<Args>(args)...)) {
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return static_cast<const First&>(*this)(std::forward<Args>(args)...);
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}
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template <
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typename... Args,
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typename = std::enable_if_t<!is_callable_v<First&, Args&&...>>>
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auto operator()(Args&&... args)
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-> decltype(std::declval<Others&>()(std::forward<Args>(args)...)) {
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return static_cast<Others&>(*this)(std::forward<Args>(args)...);
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}
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template <
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typename... Args,
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typename = std::enable_if_t<!is_callable_v<const First&, Args&&...>>>
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auto operator()(Args&&... args) const
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-> decltype(std::declval<const Others&>()(std::forward<Args>(args)...)) {
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return static_cast<const Others&>(*this)(std::forward<Args>(args)...);
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}
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};
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} // namespace details
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template <typename Function>
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Function overload(Function &&function) {
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return std::forward<Function>(function);
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}
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template <typename ...Functions, typename = std::enable_if_t<(sizeof...(Functions) > 1)>>
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auto overload(Functions ...functions) {
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return details::overloaded<Functions...>(std::move(functions)...);
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}
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} // namespace base
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