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Telegram/lib_rpl/rpl/then.h

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+// This file is part of Desktop App Toolkit,
+// a set of libraries for developing nice desktop applications.
+//
+// For license and copyright information please follow this link:
+// https://github.com/desktop-app/legal/blob/master/LEGAL
+//
+#pragma once
+
+#include <rpl/producer.h>
+
+namespace rpl {
+namespace details {
+
+template <typename Value, typename Error, typename Generator>
+class then_helper {
+public:
+	then_helper(producer<Value, Error, Generator> &&following)
+	: _following(std::move(following)) {
+	}
+
+	template <
+		typename OtherValue,
+		typename OtherError,
+		typename OtherGenerator,
+		typename NewValue = superset_type_t<Value, OtherValue>,
+		typename NewError = superset_type_t<Error, OtherError>>
+	auto operator()(
+		producer<OtherValue, OtherError, OtherGenerator> &&initial
+	) {
+		return make_producer<NewValue, NewError>([
+			initial = std::move(initial),
+			following = std::move(_following)
+		](const auto &consumer) mutable {
+			return std::move(initial).start(
+			[consumer](auto &&value) {
+				consumer.put_next_forward(
+					std::forward<decltype(value)>(value));
+			}, [consumer](auto &&error) {
+				consumer.put_error_forward(
+					std::forward<decltype(error)>(error));
+			}, [
+				consumer,
+				following = std::move(following)
+			]() mutable {
+				consumer.add_lifetime(std::move(following).start(
+				[consumer](auto &&value) {
+					consumer.put_next_forward(
+						std::forward<decltype(value)>(value));
+				}, [consumer](auto &&error) {
+					consumer.put_error_forward(
+						std::forward<decltype(error)>(error));
+				}, [consumer] {
+					consumer.put_done();
+				}));
+			});
+		});
+	}
+
+private:
+	producer<Value, Error, Generator> _following;
+
+};
+
+} // namespace details
+template <typename Value, typename Error, typename Generator>
+inline auto then(producer<Value, Error, Generator> &&following)
+-> details::then_helper<Value, Error, Generator> {
+	return { std::move(following) };
+}
+
+} // namespace rpl