51 lines
1.3 KiB
C++
51 lines
1.3 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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#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 distinct_until_changed_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<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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std::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 (!(*previous) || (**previous) != value) {
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*previous = value;
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consumer.put_next_forward(std::forward<decltype(value)>(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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} // namespace details
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inline auto distinct_until_changed()
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-> details::distinct_until_changed_helper {
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return details::distinct_until_changed_helper();
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}
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} // namespace rpl
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