tdesktop/Telegram/SourceFiles/rpl/distinct_until_changed.h

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/*
This file is part of Telegram Desktop,
the official desktop application for the Telegram messaging service.
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For license and copyright information please follow this link:
https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
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*/
#pragma once
#include <rpl/producer.h>
#include "base/optional.h"
namespace rpl {
namespace details {
class distinct_until_changed_helper {
public:
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template <typename Value, typename Error, typename Generator>
auto operator()(
producer<Value, Error, Generator> &&initial) const {
return make_producer<Value, Error>([
initial = std::move(initial)
](const auto &consumer) mutable {
auto previous = consumer.template make_state<
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std::optional<Value>
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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) {
*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) {
consumer.put_error_forward(std::forward<decltype(error)>(error));
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}, [consumer] {
consumer.put_done();
});
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});
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}
};
} // namespace details
inline auto distinct_until_changed()
-> details::distinct_until_changed_helper {
return details::distinct_until_changed_helper();
}
} // namespace rpl