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Telegram/lib_rpl/rpl/skip.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
+
+namespace rpl {
+namespace details {
+
+class skip_helper {
+public:
+	skip_helper(int count) : _count(count) {
+	}
+
+	template <
+		typename Value,
+		typename Error,
+		typename Generator>
+	auto operator()(producer<Value, Error, Generator> &&initial) {
+		return make_producer<Value, Error>([
+			initial = std::move(initial),
+			skipping = _count
+		](const auto &consumer) mutable {
+			auto count = consumer.template make_state<int>(skipping);
+			auto initial_consumer = make_consumer<Value, Error>(
+			[consumer, count](auto &&value) {
+				if (*count) {
+					--*count;
+				} else {
+					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();
+			});
+			consumer.add_lifetime(initial_consumer.terminator());
+			return std::move(initial).start_existing(initial_consumer);
+		});
+	}
+
+private:
+	int _count = 0;
+
+};
+
+} // namespace details
+
+inline auto skip(int count)
+-> details::skip_helper {
+	Expects(count >= 0);
+
+	return details::skip_helper(count);
+}
+
+} // namespace rpl