135 lines
3.5 KiB
C++
135 lines
3.5 KiB
C++
/*
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This file is part of Telegram Desktop,
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the official desktop version of Telegram messaging app, see https://telegram.org
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Telegram Desktop is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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It is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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In addition, as a special exception, the copyright holders give permission
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to link the code of portions of this program with the OpenSSL library.
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Full license: https://github.com/telegramdesktop/tdesktop/blob/master/LICENSE
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Copyright (c) 2014-2017 John Preston, https://desktop.telegram.org
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*/
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#pragma once
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#include <rpl/producer.h>
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#include <rpl/event_stream.h>
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namespace rpl {
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namespace details {
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template <typename A, typename B>
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struct supports_equality_compare {
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template <typename U, typename V>
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static auto test(const U *u, const V *v)
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-> decltype(*u == *v, details::true_t());
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static details::false_t test(...);
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static constexpr bool value
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= (sizeof(test(
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(std::decay_t<A>*)nullptr,
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(std::decay_t<B>*)nullptr
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)) == sizeof(details::true_t));
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};
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template <typename A, typename B>
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constexpr bool supports_equality_compare_v
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= supports_equality_compare<A, B>::value;
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} // namespace details
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template <typename Type>
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class variable final {
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public:
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variable() : _data{} {
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}
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template <
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typename OtherType,
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typename = std::enable_if_t<
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std::is_constructible_v<Type, OtherType&&>>>
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variable(OtherType &&data) : _data(std::forward<OtherType>(data)) {
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}
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template <
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typename OtherType,
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typename = std::enable_if_t<
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std::is_assignable_v<Type&, OtherType&&>>>
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variable &operator=(OtherType &&data) {
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_lifetime.destroy();
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return assign(std::forward<OtherType>(data));
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}
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template <
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typename OtherType,
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typename Error,
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typename Generator,
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typename = std::enable_if_t<
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std::is_assignable_v<Type&, OtherType>>>
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variable(producer<OtherType, Error, Generator> &&stream) {
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std::move(stream)
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| start_with_next([this](auto &&data) {
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assign(std::forward<decltype(data)>(data));
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}, _lifetime);
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}
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template <
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typename OtherType,
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typename Error,
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typename Generator,
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typename = std::enable_if_t<
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std::is_assignable_v<Type&, OtherType>>>
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variable &operator=(
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producer<OtherType, Error, Generator> &&stream) {
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_lifetime.destroy();
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std::move(stream)
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| start_with_next([this](auto &&data) {
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assign(std::forward<decltype(data)>(data));
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}, _lifetime);
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}
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Type current() const {
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return _data;
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}
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auto value() const {
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return _changes.events_starting_with_copy(_data);
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}
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auto changes() const {
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return _changes.events();
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}
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private:
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template <typename OtherType>
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variable &assign(OtherType &&data) {
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if constexpr (details::supports_equality_compare_v<Type, OtherType>) {
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if (!(_data == data)) {
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_data = std::forward<OtherType>(data);
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_changes.fire_copy(_data);
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}
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} else if constexpr (details::supports_equality_compare_v<Type, Type>) {
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auto old = std::move(_data);
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_data = std::forward<OtherType>(data);
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if (!(_data == old)) {
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_changes.fire_copy(_data);
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}
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} else {
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_data = std::forward<OtherType>(data);
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_changes.fire_copy(_data);
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}
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return *this;
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}
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Type _data;
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event_stream<Type> _changes;
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lifetime _lifetime;
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};
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} // namespace rpl
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