121 lines
3.5 KiB
C++
121 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 "base/optional.h"
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namespace rpl {
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namespace details {
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class combine_previous_helper {
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public:
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template <typename Value, typename Error, typename Generator>
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auto operator()(
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producer<Value, Error, Generator> &&initial) const {
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return make_producer<std::tuple<Value, Value>, Error>([
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initial = std::move(initial)
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](const auto &consumer) mutable {
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auto previous = consumer.template make_state<
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base::optional<Value>
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>();
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return std::move(initial).start(
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[consumer, previous](auto &&value) {
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if (auto exists = *previous) {
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auto &existing = *exists;
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auto next = std::make_tuple(
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std::move(existing),
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value);
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consumer.put_next(std::move(next));
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existing = std::forward<decltype(value)>(
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value);
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} else {
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*previous = std::forward<decltype(value)>(
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value);
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}
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}, [consumer](auto &&error) {
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consumer.put_error_forward(std::forward<decltype(error)>(error));
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}, [consumer] {
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consumer.put_done();
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});
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});
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}
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};
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template <typename DefaultValue>
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class combine_previous_with_default_helper {
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public:
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template <typename OtherValue>
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combine_previous_with_default_helper(OtherValue &&value)
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: _value(std::forward<OtherValue>(value)) {
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}
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template <typename Value, typename Error, typename Generator>
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auto operator()(producer<Value, Error, Generator> &&initial) {
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return make_producer<std::tuple<Value, Value>, Error>([
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initial = std::move(initial),
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value = Value(std::move(_value))
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](const auto &consumer) mutable {
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auto previous = consumer.template make_state<Value>(
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std::move(value));
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return std::move(initial).start(
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[consumer, previous](auto &&value) {
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auto &existing = *previous;
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auto next = std::make_tuple(
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std::move(existing),
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value);
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consumer.put_next(std::move(next));
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existing = std::forward<decltype(value)>(value);
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}, [consumer](auto &&error) {
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consumer.put_error_forward(std::forward<decltype(error)>(error));
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}, [consumer] {
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consumer.put_done();
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});
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});
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}
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private:
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DefaultValue _value;
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};
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template <typename DefaultValue>
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combine_previous_with_default_helper<std::decay_t<DefaultValue>>
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combine_previous_with_default(DefaultValue &&value) {
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return { std::forward<DefaultValue>(value) };
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}
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} // namespace details
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inline auto combine_previous()
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-> details::combine_previous_helper {
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return details::combine_previous_helper();
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}
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template <typename DefaultValue>
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inline auto combine_previous(DefaultValue &&value) {
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return details::combine_previous_with_default(
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std::forward<DefaultValue>(value));
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}
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} // namespace rpl
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