From 80d9938e96a688c860fd84225091492eb6d8e246 Mon Sep 17 00:00:00 2001
From: John Preston <johnprestonmail@gmail.com>
Date: Wed, 27 Sep 2017 18:15:26 +0300
Subject: [PATCH] Support and use not type-erased consumers.

---
 Telegram/SourceFiles/base/observer.h          |   4 +-
 .../info/profile/info_profile_values.cpp      |   2 +-
 Telegram/SourceFiles/rpl/after_next.h         |   2 +-
 Telegram/SourceFiles/rpl/combine.h            |  71 +-
 Telegram/SourceFiles/rpl/combine_previous.h   |  10 +-
 Telegram/SourceFiles/rpl/complete.h           |   3 +-
 Telegram/SourceFiles/rpl/consumer.h           | 813 ++++++++++++------
 Telegram/SourceFiles/rpl/deferred.h           |   2 +-
 .../SourceFiles/rpl/distinct_until_changed.h  |   2 +-
 Telegram/SourceFiles/rpl/event_stream.h       |   3 +-
 Telegram/SourceFiles/rpl/fail.h               |   3 +-
 Telegram/SourceFiles/rpl/filter.h             |   6 +-
 Telegram/SourceFiles/rpl/flatten_latest.h     |   3 +-
 Telegram/SourceFiles/rpl/map.h                |  28 +-
 Telegram/SourceFiles/rpl/never.h              |   4 +-
 Telegram/SourceFiles/rpl/producer.h           |  22 +-
 Telegram/SourceFiles/rpl/range.h              |  16 +-
 Telegram/SourceFiles/rpl/then.h               |   3 +-
 18 files changed, 651 insertions(+), 346 deletions(-)

diff --git a/Telegram/SourceFiles/base/observer.h b/Telegram/SourceFiles/base/observer.h
index 79f8149b3c..81a394a13b 100644
--- a/Telegram/SourceFiles/base/observer.h
+++ b/Telegram/SourceFiles/base/observer.h
@@ -466,7 +466,7 @@ template <
 	typename = std::enable_if_t<!std::is_same_v<Type, void>>>
 inline auto ObservableViewer(base::Observable<Type> &observable) {
 	return rpl::make_producer<Type>([&observable](
-			const rpl::consumer<Type> &consumer) {
+			const auto &consumer) {
 		auto lifetime = rpl::lifetime();
 		lifetime.make_state<base::Subscription>(
 			observable.add_subscription([consumer](auto &&update) {
@@ -479,7 +479,7 @@ inline auto ObservableViewer(base::Observable<Type> &observable) {
 
 inline auto ObservableViewer(base::Observable<void> &observable) {
 	return rpl::make_producer<>([&observable](
-			const rpl::consumer<> &consumer) {
+			const auto &consumer) {
 		auto lifetime = rpl::lifetime();
 		lifetime.make_state<base::Subscription>(
 			observable.add_subscription([consumer]() {
diff --git a/Telegram/SourceFiles/info/profile/info_profile_values.cpp b/Telegram/SourceFiles/info/profile/info_profile_values.cpp
index a6d7d0d9f1..f9f036e013 100644
--- a/Telegram/SourceFiles/info/profile/info_profile_values.cpp
+++ b/Telegram/SourceFiles/info/profile/info_profile_values.cpp
@@ -34,7 +34,7 @@ namespace Profile {
 
 rpl::producer<Notify::PeerUpdate> PeerUpdateViewer(
 		Notify::PeerUpdate::Flags flags) {
-	return [=](const rpl::consumer<Notify::PeerUpdate> &consumer) {
+	return [=](const auto &consumer) {
 		auto lifetime = rpl::lifetime();
 		lifetime.make_state<base::Subscription>(
 			Notify::PeerUpdated().add_subscription({ flags, [=](
diff --git a/Telegram/SourceFiles/rpl/after_next.h b/Telegram/SourceFiles/rpl/after_next.h
index 5ceee13e4b..6ddb0cd178 100644
--- a/Telegram/SourceFiles/rpl/after_next.h
+++ b/Telegram/SourceFiles/rpl/after_next.h
@@ -38,7 +38,7 @@ public:
 		return make_producer<Value, Error>([
 			initial = std::move(initial),
 			method = std::move(_method)
-		](const consumer<Value, Error> &consumer) mutable {
+		](const auto &consumer) mutable {
 			return std::move(initial).start(
 			[method = std::move(method), consumer](auto &&value) {
 				auto copy = method;
diff --git a/Telegram/SourceFiles/rpl/combine.h b/Telegram/SourceFiles/rpl/combine.h
index 5e001483fc..2d16bf9432 100644
--- a/Telegram/SourceFiles/rpl/combine.h
+++ b/Telegram/SourceFiles/rpl/combine.h
@@ -107,7 +107,7 @@ inline void combine_subscribe(
 		const consumer_type &consumer,
 		combine_state<Values...> *state,
 		std::index_sequence<I...>,
-		producer<Values, Errors, Generators> &&...producers) {
+		std::tuple<producer<Values, Errors, Generators>...> &&saved) {
 	auto consume = { (
 		details::combine_subscribe_one<
 			I,
@@ -116,10 +116,53 @@ inline void combine_subscribe(
 		>(
 			consumer,
 			state
-		).subscribe(std::move(producers)), 0)... };
+		).subscribe(std::get<I>(std::move(saved))), 0)... };
 	(void)consume;
 }
 
+template <typename ...Producers>
+class combine_implementation_helper;
+
+template <typename ...Producers>
+combine_implementation_helper<std::decay_t<Producers>...>
+make_combine_implementation_helper(Producers &&...producers) {
+	return combine_implementation_helper<std::decay_t<Producers>...>(
+		std::forward<Producers>(producers)...);
+}
+
+template <
+	typename ...Values,
+	typename ...Errors,
+	typename ...Generators>
+class combine_implementation_helper<producer<Values, Errors, Generators>...> {
+public:
+	using CombinedValue = std::tuple<Values...>;
+	using CombinedError = details::normalized_variant_t<Errors...>;
+
+	combine_implementation_helper(
+		producer<Values, Errors, Generators> &&...producers)
+	: _saved(std::make_tuple(std::move(producers)...)) {
+	}
+
+	template <typename Handlers>
+	lifetime operator()(const consumer<CombinedValue, CombinedError, Handlers> &consumer) {
+		auto state = consumer.template make_state<
+			details::combine_state<Values...>>();
+		constexpr auto kArity = sizeof...(Values);
+		details::combine_subscribe(
+			consumer,
+			state,
+			std::make_index_sequence<kArity>(),
+			std::move(_saved));
+
+		return lifetime();
+	}
+
+private:
+	std::tuple<producer<Values, Errors, Generators>...> _saved;
+
+};
+
 template <
 	typename ...Values,
 	typename ...Errors,
@@ -128,26 +171,9 @@ inline auto combine_implementation(
 		producer<Values, Errors, Generators> &&...producers) {
 	using CombinedValue = std::tuple<Values...>;
 	using CombinedError = details::normalized_variant_t<Errors...>;
-	using consumer_type = consumer<CombinedValue, CombinedError>;
-	auto result = [](
-			const consumer_type &consumer,
-			producer<Values, Errors, Generators> &...producers) {
-		auto state = consumer.template make_state<
-			details::combine_state<Values...>>();
 
-		constexpr auto kArity = sizeof...(Values);
-		details::combine_subscribe(
-			consumer,
-			state,
-			std::make_index_sequence<kArity>(),
-			std::move(producers)...);
-
-		return lifetime();
-	};
-	return make_producer<CombinedValue, CombinedError>(std::bind(
-		result,
-		std::placeholders::_1,
-		std::move(producers)...));
+	return make_producer<CombinedValue, CombinedError>(
+		make_combine_implementation_helper(std::move(producers)...));
 }
 
 template <typename ...Args>
@@ -290,10 +316,9 @@ template <typename Value, typename Error, typename Generator>
 inline auto combine(
 		std::vector<producer<Value, Error, Generator>> &&producers) {
 	using state_type = details::combine_vector_state<Value>;
-	using consumer_type = consumer<std::vector<Value>, Error>;
 	return make_producer<std::vector<Value>, Error>([
 		producers = std::move(producers)
-	](const consumer_type &consumer) mutable {
+	](const auto &consumer) mutable {
 		auto count = producers.size();
 		auto state = consumer.template make_state<state_type>();
 		state->accumulated.resize(count);
diff --git a/Telegram/SourceFiles/rpl/combine_previous.h b/Telegram/SourceFiles/rpl/combine_previous.h
index f74a209980..93f593b1c7 100644
--- a/Telegram/SourceFiles/rpl/combine_previous.h
+++ b/Telegram/SourceFiles/rpl/combine_previous.h
@@ -31,12 +31,9 @@ public:
 	template <typename Value, typename Error, typename Generator>
 	auto operator()(
 			producer<Value, Error, Generator> &&initial) const {
-		using consumer_type = consumer<
-			std::tuple<Value, Value>,
-			Error>;
 		return make_producer<std::tuple<Value, Value>, Error>([
 			initial = std::move(initial)
-		](const consumer_type &consumer) mutable {
+		](const auto &consumer) mutable {
 			auto previous = consumer.template make_state<
 				base::optional<Value>
 			>();
@@ -74,13 +71,10 @@ public:
 
 	template <typename Value, typename Error, typename Generator>
 	auto operator()(producer<Value, Error, Generator> &&initial) {
-		using consumer_type = consumer<
-			std::tuple<Value, Value>,
-			Error>;
 		return make_producer<std::tuple<Value, Value>, Error>([
 			initial = std::move(initial),
 			value = Value(std::move(_value))
-		](const consumer_type &consumer) mutable {
+		](const auto &consumer) mutable {
 			auto previous = consumer.template make_state<Value>(
 				std::move(value));
 			return std::move(initial).start(
diff --git a/Telegram/SourceFiles/rpl/complete.h b/Telegram/SourceFiles/rpl/complete.h
index ada04f8642..0205db739b 100644
--- a/Telegram/SourceFiles/rpl/complete.h
+++ b/Telegram/SourceFiles/rpl/complete.h
@@ -26,8 +26,7 @@ namespace rpl {
 
 template <typename Value = empty_value, typename Error = no_error>
 inline auto complete() {
-	return make_producer<Value, Error>([](
-			const consumer<Value, Error> &consumer) {
+	return make_producer<Value, Error>([](const auto &consumer) {
 		consumer.put_done();
 		return lifetime();
 	});
diff --git a/Telegram/SourceFiles/rpl/consumer.h b/Telegram/SourceFiles/rpl/consumer.h
index f39369b03c..7f65f8b2dd 100644
--- a/Telegram/SourceFiles/rpl/consumer.h
+++ b/Telegram/SourceFiles/rpl/consumer.h
@@ -25,6 +25,241 @@ Copyright (c) 2014-2017 John Preston, https://desktop.telegram.org
 #include <rpl/details/callable.h>
 
 namespace rpl {
+namespace details {
+
+template <
+	typename Value,
+	typename Error,
+	typename OnNext,
+	typename OnError,
+	typename OnDone>
+class consumer_handlers;
+
+template <typename Value, typename Error>
+class type_erased_handlers {
+public:
+	template <
+		typename OnNext,
+		typename OnError,
+		typename OnDone>
+	static std::shared_ptr<type_erased_handlers> create(
+			OnNext &&next,
+			OnError &&error,
+			OnDone &&done) {
+		return std::make_shared<consumer_handlers<
+			Value,
+			Error,
+			std::decay_t<OnNext>,
+			std::decay_t<OnError>,
+			std::decay_t<OnDone>>>(
+				std::forward<OnNext>(next),
+				std::forward<OnError>(error),
+				std::forward<OnDone>(done));
+	}
+
+	virtual bool put_next(Value &&value) = 0;
+	virtual bool put_next_copy(const Value &value) = 0;
+	virtual void put_error(Error &&error) = 0;
+	virtual void put_error_copy(const Error &error) = 0;
+	virtual void put_done() = 0;
+
+	void add_lifetime(lifetime &&lifetime);
+
+	template <typename Type, typename... Args>
+	Type *make_state(Args&& ...args);
+
+	void terminate();
+
+protected:
+	lifetime _lifetime;
+	bool _terminated = false;
+
+};
+
+template <typename Handlers>
+struct is_type_erased_handlers
+	: std::false_type {
+};
+
+template <typename Value, typename Error>
+struct is_type_erased_handlers<type_erased_handlers<Value, Error>>
+	: std::true_type {
+};
+
+template <typename Value, typename Error, typename OnNext, typename OnError, typename OnDone>
+class consumer_handlers final
+	: public type_erased_handlers<Value, Error> {
+public:
+	template <
+		typename OnNextOther,
+		typename OnErrorOther,
+		typename OnDoneOther>
+	consumer_handlers(
+		OnNextOther &&next,
+		OnErrorOther &&error,
+		OnDoneOther &&done)
+		: _next(std::forward<OnNextOther>(next))
+		, _error(std::forward<OnErrorOther>(error))
+		, _done(std::forward<OnDoneOther>(done)) {
+	}
+
+	template <
+		typename OnNextOther,
+		typename OnErrorOther,
+		typename OnDoneOther>
+	static std::shared_ptr<consumer_handlers> create(
+			OnNextOther &&next,
+			OnErrorOther &&error,
+			OnDoneOther &&done) {
+		return std::make_shared<consumer_handlers>(
+				std::forward<OnNextOther>(next),
+				std::forward<OnErrorOther>(error),
+				std::forward<OnDoneOther>(done));
+	}
+
+	bool put_next(Value &&value) final override;
+	bool put_next_copy(const Value &value) final override;
+	void put_error(Error &&error) final override;
+	void put_error_copy(const Error &error) final override;
+	void put_done() final override;
+
+private:
+	OnNext _next;
+	OnError _error;
+	OnDone _done;
+
+};
+
+template <typename Value, typename Error>
+inline void type_erased_handlers<Value, Error>::add_lifetime(
+		lifetime &&lifetime) {
+	if (_terminated) {
+		lifetime.destroy();
+	} else {
+		_lifetime.add(std::move(lifetime));
+	}
+}
+
+template <typename Value, typename Error>
+template <typename Type, typename... Args>
+inline Type *type_erased_handlers<Value, Error>::make_state(
+		Args&& ...args) {
+	Expects(!_terminated);
+	return _lifetime.make_state<Type>(std::forward<Args>(args)...);
+}
+
+template <typename Value, typename Error>
+inline void type_erased_handlers<Value, Error>::terminate() {
+	if (!_terminated) {
+		_terminated = true;
+		base::take(_lifetime).destroy();
+	}
+}
+
+template <
+	typename Value,
+	typename Error,
+	typename OnNext,
+	typename OnError,
+	typename OnDone>
+bool consumer_handlers<
+	Value,
+	Error,
+	OnNext,
+	OnError,
+	OnDone
+>::put_next(Value &&value) {
+	if (this->_terminated) {
+		return false;
+	}
+	auto handler = this->_next;
+	details::callable_invoke(std::move(handler), std::move(value));
+	return true;
+}
+
+template <
+	typename Value,
+	typename Error,
+	typename OnNext,
+	typename OnError,
+	typename OnDone>
+bool consumer_handlers<
+	Value,
+	Error,
+	OnNext,
+	OnError,
+	OnDone
+>::put_next_copy(const Value &value) {
+	if (this->_terminated) {
+		return false;
+	}
+	auto handler = this->_next;
+	details::const_ref_call_invoke(std::move(handler), value);
+	return true;
+}
+
+template <
+	typename Value,
+	typename Error,
+	typename OnNext,
+	typename OnError,
+	typename OnDone>
+void consumer_handlers<
+	Value,
+	Error,
+	OnNext,
+	OnError,
+	OnDone
+>::put_error(Error &&error) {
+	if (!this->_terminated) {
+		details::callable_invoke(
+			std::move(this->_error),
+			std::move(error));
+		this->terminate();
+	}
+}
+
+template <
+	typename Value,
+	typename Error,
+	typename OnNext,
+	typename OnError,
+	typename OnDone>
+void consumer_handlers<
+	Value,
+	Error,
+	OnNext,
+	OnError,
+	OnDone
+>::put_error_copy(const Error &error) {
+	if (!this->_terminated) {
+		details::const_ref_call_invoke(
+			std::move(this->_error),
+			error);
+		this->terminate();
+	}
+}
+
+template <
+	typename Value,
+	typename Error,
+	typename OnNext,
+	typename OnError,
+	typename OnDone>
+void consumer_handlers<
+	Value,
+	Error,
+	OnNext,
+	OnError,
+	OnDone
+>::put_done() {
+	if (!this->_terminated) {
+		std::move(this->_done)();
+		this->terminate();
+	}
+}
+
+} // namespace details
 
 struct no_value {
 	no_value() = delete;
@@ -40,19 +275,24 @@ struct empty_value {
 struct empty_error {
 };
 
-template <typename Value = empty_value, typename Error = no_error>
-class consumer {
+template <
+	typename Value = empty_value,
+	typename Error = no_error,
+	typename Handlers = details::type_erased_handlers<Value, Error>>
+class consumer;
+
+namespace details {
+
+template <typename Value, typename Error, typename Handlers>
+class consumer_base {
+	using is_type_erased = is_type_erased_handlers<Handlers>;
+
 public:
 	template <
 		typename OnNext,
 		typename OnError,
-		typename OnDone,
-		typename = std::enable_if_t<
-			details::is_callable_v<OnNext, Value>>,
-		typename = decltype(std::declval<OnError>()(
-			std::declval<Error>())),
-		typename = decltype(std::declval<OnDone>()())>
-	consumer(
+		typename OnDone>
+	consumer_base(
 		OnNext &&next,
 		OnError &&error,
 		OnDone &&done);
@@ -82,104 +322,322 @@ public:
 
 	void terminate() const;
 
-	bool operator==(const consumer &other) const {
-		return _instance == other._instance;
-	}
-	bool operator!=(const consumer &other) const {
-		return !(*this == other);
-	}
-	bool operator<(const consumer &other) const {
-		return _instance < other._instance;
-	}
-	bool operator>(const consumer &other) const {
-		return other < *this;
-	}
-	bool operator<=(const consumer &other) const {
-		return !(other < *this);
-	}
-	bool operator>=(const consumer &other) const {
-		return !(*this < other);
+	const details::type_erased_handlers<Value, Error> *comparable() const {
+		return _handlers.get();
 	}
 
 private:
-	class abstract_instance;
-
-	template <typename OnNext, typename OnError, typename OnDone>
-	class instance;
-
-	template <typename OnNext, typename OnError, typename OnDone>
-	std::shared_ptr<abstract_instance> ConstructInstance(
-		OnNext &&next,
-		OnError &&error,
-		OnDone &&done);
-
-	mutable std::shared_ptr<abstract_instance> _instance;
-
-};
-
-
-template <typename Value, typename Error>
-class consumer<Value, Error>::abstract_instance {
-public:
-	virtual bool put_next(Value &&value) = 0;
-	virtual bool put_next_copy(const Value &value) = 0;
-	virtual void put_error(Error &&error) = 0;
-	virtual void put_error_copy(const Error &error) = 0;
-	virtual void put_done() = 0;
-
-	void add_lifetime(lifetime &&lifetime);
-
-	template <typename Type, typename... Args>
-	Type *make_state(Args&& ...args);
-
-	void terminate();
-
-protected:
-	lifetime _lifetime;
-	bool _terminated = false;
-
-};
-
-template <typename Value, typename Error>
-template <typename OnNext, typename OnError, typename OnDone>
-class consumer<Value, Error>::instance
-	: public consumer<Value, Error>::abstract_instance {
-public:
 	template <
-		typename OnNextImpl,
-		typename OnErrorImpl,
-		typename OnDoneImpl>
-	instance(
-		OnNextImpl &&next,
-		OnErrorImpl &&error,
-		OnDoneImpl &&done)
-		: _next(std::forward<OnNextImpl>(next))
-		, _error(std::forward<OnErrorImpl>(error))
-		, _done(std::forward<OnDoneImpl>(done)) {
+		typename OtherHandlers,
+		typename = std::enable_if_t<
+			std::is_base_of_v<Handlers, OtherHandlers>>>
+	consumer_base(const std::shared_ptr<OtherHandlers> &handlers)
+	: _handlers(handlers) {
 	}
 
-	bool put_next(Value &&value) override;
-	bool put_next_copy(const Value &value) override;
-	void put_error(Error &&error) override;
-	void put_error_copy(const Error &error) override;
-	void put_done() override;
+	template <
+		typename OtherHandlers,
+		typename = std::enable_if_t<
+			std::is_base_of_v<Handlers, OtherHandlers>>>
+	consumer_base(std::shared_ptr<OtherHandlers> &&handlers)
+	: _handlers(std::move(handlers)) {
+	}
 
-private:
-	OnNext _next;
-	OnError _error;
-	OnDone _done;
+	mutable std::shared_ptr<Handlers> _handlers;
+
+	bool handlers_put_next(Value &&value, std::true_type) const {
+		return _handlers->put_next(std::move(value));
+	}
+	bool handlers_put_next_copy(
+			const Value &value,
+			std::true_type) const {
+		return _handlers->put_next_copy(value);
+	}
+	void handlers_put_error(Error &&error, std::true_type) const {
+		return std::exchange(_handlers, nullptr)->put_error(std::move(error));
+	}
+	void handlers_put_error_copy(
+			const Error &error,
+			std::true_type) const {
+		return std::exchange(_handlers, nullptr)->put_error_copy(error);
+	}
+	void handlers_put_done(std::true_type) const {
+		return std::exchange(_handlers, nullptr)->put_done();
+	}
+
+	bool handlers_put_next(Value &&value, std::false_type) const {
+		return _handlers->Handlers::put_next(std::move(value));
+	}
+	bool handlers_put_next_copy(
+			const Value &value,
+			std::false_type) const {
+		return _handlers->Handlers::put_next_copy(value);
+	}
+	void handlers_put_error(Error &&error, std::false_type) const {
+		return std::exchange(_handlers, nullptr)->Handlers::put_error(std::move(error));
+	}
+	void handlers_put_error_copy(
+			const Error &error,
+			std::false_type) const {
+		return std::exchange(_handlers, nullptr)->Handlers::put_error_copy(error);
+	}
+	void handlers_put_done(std::false_type) const {
+		return std::exchange(_handlers, nullptr)->Handlers::put_done();
+	}
+
+	template <
+		typename OtherValue,
+		typename OtherError,
+		typename OtherHandlers>
+	friend class ::rpl::consumer;
+
+};
+
+template <typename Value, typename Error, typename Handlers>
+template <typename OnNext, typename OnError, typename OnDone>
+inline consumer_base<Value, Error, Handlers>::consumer_base(
+	OnNext &&next,
+	OnError &&error,
+	OnDone &&done) : _handlers(Handlers::create(
+		std::forward<OnNext>(next),
+		std::forward<OnError>(error),
+		std::forward<OnDone>(done))) {
+}
+
+template <typename Value, typename Error, typename Handlers>
+inline bool consumer_base<Value, Error, Handlers>::put_next(
+		Value &&value) const {
+	if (_handlers) {
+		if (handlers_put_next(std::move(value), is_type_erased())) {
+			return true;
+		}
+		_handlers = nullptr;
+	}
+	return false;
+}
+
+template <typename Value, typename Error, typename Handlers>
+inline bool consumer_base<Value, Error, Handlers>::put_next_copy(
+		const Value &value) const {
+	if (_handlers) {
+		if (handlers_put_next_copy(value, is_type_erased())) {
+			return true;
+		}
+		_handlers = nullptr;
+	}
+	return false;
+}
+
+template <typename Value, typename Error, typename Handlers>
+inline void consumer_base<Value, Error, Handlers>::put_error(
+		Error &&error) const {
+	if (_handlers) {
+		handlers_put_error(std::move(error), is_type_erased());
+	}
+}
+
+template <typename Value, typename Error, typename Handlers>
+inline void consumer_base<Value, Error, Handlers>::put_error_copy(
+		const Error &error) const {
+	if (_handlers) {
+		handlers_put_error_copy(error, is_type_erased());
+	}
+}
+
+template <typename Value, typename Error, typename Handlers>
+inline void consumer_base<Value, Error, Handlers>::put_done() const {
+	if (_handlers) {
+		handlers_put_done(is_type_erased());
+	}
+}
+
+template <typename Value, typename Error, typename Handlers>
+inline void consumer_base<Value, Error, Handlers>::add_lifetime(
+		lifetime &&lifetime) const {
+	if (_handlers) {
+		_handlers->add_lifetime(std::move(lifetime));
+	} else {
+		lifetime.destroy();
+	}
+}
+
+template <typename Value, typename Error, typename Handlers>
+template <typename Type, typename... Args>
+inline Type *consumer_base<Value, Error, Handlers>::make_state(
+		Args&& ...args) const {
+	Expects(_handlers != nullptr);
+	return _handlers->template make_state<Type>(
+		std::forward<Args>(args)...);
+}
+
+template <typename Value, typename Error, typename Handlers>
+inline void consumer_base<Value, Error, Handlers>::terminate() const {
+	if (_handlers) {
+		std::exchange(_handlers, nullptr)->terminate();
+	}
+}
+
+template <typename Value, typename Error>
+using consumer_base_type_erased = consumer_base<
+	Value,
+	Error,
+	details::type_erased_handlers<Value, Error>>;
+
+template <typename Value, typename Error, typename Handlers>
+constexpr bool is_specific_handlers_v = !std::is_same_v<
+	details::type_erased_handlers<Value, Error>,
+	Handlers
+> && std::is_base_of_v<
+	details::type_erased_handlers<Value, Error>,
+	Handlers
+>;
+
+} // namespace details
+
+template <typename Value, typename Error, typename Handlers>
+class consumer final
+: public details::consumer_base<Value, Error, Handlers> {
+	using parent_type = details::consumer_base<
+		Value,
+		Error,
+		Handlers>;
+
+public:
+	using parent_type::parent_type;
 
 };
 
 template <typename Value, typename Error>
-template <typename OnNext, typename OnError, typename OnDone>
-inline std::shared_ptr<
-	typename consumer<Value, Error>::abstract_instance>
-consumer<Value, Error>::ConstructInstance(
+class consumer<Value, Error, details::type_erased_handlers<Value, Error>> final
+: public details::consumer_base_type_erased<Value, Error> {
+	using parent_type = details::consumer_base_type_erased<
+		Value,
+		Error>;
+
+public:
+	using parent_type::parent_type;
+
+	template <
+		typename Handlers,
+		typename = std::enable_if_t<
+			details::is_specific_handlers_v<Value, Error, Handlers>>>
+	consumer(const details::consumer_base<Value, Error, Handlers> &other)
+	: parent_type(other._handlers) {
+	}
+
+	template <
+		typename Handlers,
+		typename = std::enable_if_t<
+			details::is_specific_handlers_v<Value, Error, Handlers>>>
+	consumer(details::consumer_base<Value, Error, Handlers> &&other)
+	: parent_type(std::move(other._handlers)) {
+	}
+
+	template <
+		typename Handlers,
+		typename = std::enable_if_t<
+			details::is_specific_handlers_v<Value, Error, Handlers>>>
+	consumer &operator=(
+			const details::consumer_base<Value, Error, Handlers> &other) {
+		_handlers = other._handlers;
+		return *this;
+	}
+
+	template <
+		typename Handlers,
+		typename = std::enable_if_t<
+			details::is_specific_handlers_v<Value, Error, Handlers>>>
+	consumer &operator=(
+			details::consumer_base<Value, Error, Handlers> &&other) {
+		_handlers = std::move(other._handlers);
+		return *this;
+	}
+
+};
+
+template <
+	typename Value,
+	typename Error,
+	typename Handlers1,
+	typename Handlers2>
+inline bool operator==(
+		const consumer<Value, Error, Handlers1> &a,
+		const consumer<Value, Error, Handlers2> &b) {
+	return a.comparable() == b.comparable();
+}
+
+template <
+	typename Value,
+	typename Error,
+	typename Handlers1,
+	typename Handlers2>
+inline bool operator<(
+		const consumer<Value, Error, Handlers1> &a,
+		const consumer<Value, Error, Handlers2> &b) {
+	return a.comparable() < b.comparable();
+}
+
+template <
+	typename Value,
+	typename Error,
+	typename Handlers1,
+	typename Handlers2>
+inline bool operator!=(
+		const consumer<Value, Error, Handlers1> &a,
+		const consumer<Value, Error, Handlers2> &b) {
+	return !(a == b);
+}
+
+template <
+	typename Value,
+	typename Error,
+	typename Handlers1,
+	typename Handlers2>
+inline bool operator>(
+		const consumer<Value, Error, Handlers1> &a,
+		const consumer<Value, Error, Handlers2> &b) {
+	return b < a;
+}
+
+template <
+	typename Value,
+	typename Error,
+	typename Handlers1,
+	typename Handlers2>
+inline bool operator<=(
+		const consumer<Value, Error, Handlers1> &a,
+		const consumer<Value, Error, Handlers2> &b) {
+	return !(b < a);
+}
+
+template <
+	typename Value,
+	typename Error,
+	typename Handlers1,
+	typename Handlers2>
+inline bool operator>=(
+		const consumer<Value, Error, Handlers1> &a,
+		const consumer<Value, Error, Handlers2> &b) {
+	return !(a < b);
+}
+
+template <
+	typename Value,
+	typename Error,
+	typename OnNext,
+	typename OnError,
+	typename OnDone,
+	typename = std::enable_if_t<
+		details::is_callable_v<OnNext, Value> &&
+		details::is_callable_v<OnError, Error> &&
+		details::is_callable_v<OnDone>>>
+inline auto make_consumer(
 		OnNext &&next,
 		OnError &&error,
 		OnDone &&done) {
-	return std::make_shared<instance<
+	return consumer<Value, Error, details::consumer_handlers<
+		Value,
+		Error,
 		std::decay_t<OnNext>,
 		std::decay_t<OnError>,
 		std::decay_t<OnDone>>>(
@@ -188,173 +646,4 @@ consumer<Value, Error>::ConstructInstance(
 			std::forward<OnDone>(done));
 }
 
-template <typename Value, typename Error>
-template <
-	typename OnNext,
-	typename OnError,
-	typename OnDone,
-	typename,
-	typename,
-	typename>
-inline consumer<Value, Error>::consumer(
-	OnNext &&next,
-	OnError &&error,
-	OnDone &&done) : _instance(ConstructInstance(
-		std::forward<OnNext>(next),
-		std::forward<OnError>(error),
-		std::forward<OnDone>(done))) {
-}
-
-template <typename Value, typename Error>
-inline bool consumer<Value, Error>::put_next(Value &&value) const {
-	if (_instance) {
-		if (_instance->put_next(std::move(value))) {
-			return true;
-		}
-		_instance = nullptr;
-	}
-	return false;
-}
-
-template <typename Value, typename Error>
-inline bool consumer<Value, Error>::put_next_copy(
-		const Value &value) const {
-	if (_instance) {
-		if (_instance->put_next_copy(value)) {
-			return true;
-		}
-		_instance = nullptr;
-	}
-	return false;
-}
-
-template <typename Value, typename Error>
-inline void consumer<Value, Error>::put_error(Error &&error) const {
-	if (_instance) {
-		std::exchange(_instance, nullptr)->put_error(
-			std::move(error));
-	}
-}
-
-template <typename Value, typename Error>
-inline void consumer<Value, Error>::put_error_copy(
-		const Error &error) const {
-	if (_instance) {
-		std::exchange(_instance, nullptr)->put_error_copy(error);
-	}
-}
-
-template <typename Value, typename Error>
-inline void consumer<Value, Error>::put_done() const {
-	if (_instance) {
-		std::exchange(_instance, nullptr)->put_done();
-	}
-}
-
-template <typename Value, typename Error>
-inline void consumer<Value, Error>::add_lifetime(lifetime &&lifetime) const {
-	if (_instance) {
-		_instance->add_lifetime(std::move(lifetime));
-	} else {
-		lifetime.destroy();
-	}
-}
-
-template <typename Value, typename Error>
-template <typename Type, typename... Args>
-inline Type *consumer<Value, Error>::make_state(Args&& ...args) const {
-	Expects(_instance != nullptr);
-	return _instance->template make_state<Type>(std::forward<Args>(args)...);
-}
-
-template <typename Value, typename Error>
-inline void consumer<Value, Error>::terminate() const {
-	if (_instance) {
-		std::exchange(_instance, nullptr)->terminate();
-	}
-}
-
-template <typename Value, typename Error>
-inline void consumer<Value, Error>::abstract_instance::add_lifetime(
-		lifetime &&lifetime) {
-	if (_terminated) {
-		lifetime.destroy();
-	} else {
-		_lifetime.add(std::move(lifetime));
-	}
-}
-
-template <typename Value, typename Error>
-template <typename Type, typename... Args>
-inline Type *consumer<Value, Error>::abstract_instance::make_state(
-		Args&& ...args) {
-	Expects(!_terminated);
-	return _lifetime.make_state<Type>(std::forward<Args>(args)...);
-}
-
-template <typename Value, typename Error>
-inline void consumer<Value, Error>::abstract_instance::terminate() {
-	if (!_terminated) {
-		_terminated = true;
-		base::take(_lifetime).destroy();
-	}
-}
-
-template <typename Value, typename Error>
-template <typename OnNext, typename OnError, typename OnDone>
-bool consumer<Value, Error>::instance<OnNext, OnError, OnDone>::put_next(
-		Value &&value) {
-	if (this->_terminated) {
-		return false;
-	}
-	auto handler = this->_next;
-	details::callable_invoke(std::move(handler), std::move(value));
-	return true;
-}
-
-template <typename Value, typename Error>
-template <typename OnNext, typename OnError, typename OnDone>
-bool consumer<Value, Error>::instance<OnNext, OnError, OnDone>::put_next_copy(
-		const Value &value) {
-	if (this->_terminated) {
-		return false;
-	}
-	auto handler = this->_next;
-	details::const_ref_call_invoke(std::move(handler), value);
-	return true;
-}
-
-template <typename Value, typename Error>
-template <typename OnNext, typename OnError, typename OnDone>
-void consumer<Value, Error>::instance<OnNext, OnError, OnDone>::put_error(
-		Error &&error) {
-	if (!this->_terminated) {
-		details::callable_invoke(
-			std::move(this->_error),
-			std::move(error));
-		this->terminate();
-	}
-}
-
-template <typename Value, typename Error>
-template <typename OnNext, typename OnError, typename OnDone>
-void consumer<Value, Error>::instance<OnNext, OnError, OnDone>::put_error_copy(
-		const Error &error) {
-	if (!this->_terminated) {
-		details::const_ref_call_invoke(
-			std::move(this->_error),
-			error);
-		this->terminate();
-	}
-}
-
-template <typename Value, typename Error>
-template <typename OnNext, typename OnError, typename OnDone>
-void consumer<Value, Error>::instance<OnNext, OnError, OnDone>::put_done() {
-	if (!this->_terminated) {
-		std::move(this->_done)();
-		this->terminate();
-	}
-}
-
 } // namespace rpl
diff --git a/Telegram/SourceFiles/rpl/deferred.h b/Telegram/SourceFiles/rpl/deferred.h
index 62ae2e63f1..6d89c75e1a 100644
--- a/Telegram/SourceFiles/rpl/deferred.h
+++ b/Telegram/SourceFiles/rpl/deferred.h
@@ -31,7 +31,7 @@ template <
 inline auto deferred(Creator &&creator) {
 	return make_producer<Value, Error>([
 		creator = std::forward<Creator>(creator)
-	](const consumer<Value, Error> &consumer) mutable {
+	](const auto &consumer) mutable {
 		return std::move(creator)().start_existing(consumer);
 	});
 }
diff --git a/Telegram/SourceFiles/rpl/distinct_until_changed.h b/Telegram/SourceFiles/rpl/distinct_until_changed.h
index 329d2d35c0..35f9b92f8f 100644
--- a/Telegram/SourceFiles/rpl/distinct_until_changed.h
+++ b/Telegram/SourceFiles/rpl/distinct_until_changed.h
@@ -33,7 +33,7 @@ public:
 			producer<Value, Error, Generator> &&initial) const {
 		return make_producer<Value, Error>([
 			initial = std::move(initial)
-		](const consumer<Value, Error> &consumer) mutable {
+		](const auto &consumer) mutable {
 			auto previous = consumer.template make_state<
 				base::optional<Value>
 			>();
diff --git a/Telegram/SourceFiles/rpl/event_stream.h b/Telegram/SourceFiles/rpl/event_stream.h
index 36c0d99532..5580352d35 100644
--- a/Telegram/SourceFiles/rpl/event_stream.h
+++ b/Telegram/SourceFiles/rpl/event_stream.h
@@ -47,9 +47,8 @@ public:
 		return fire_forward(value);
 	}
 	auto events() const {
-		using consumer_type = consumer<Value, no_error>;
 		return make_producer<Value>([weak = weak()](
-			const consumer_type &consumer) {
+			const auto &consumer) {
 			if (auto strong = weak.lock()) {
 				auto result = [weak, consumer] {
 					if (auto strong = weak.lock()) {
diff --git a/Telegram/SourceFiles/rpl/fail.h b/Telegram/SourceFiles/rpl/fail.h
index 0573276230..1efc344818 100644
--- a/Telegram/SourceFiles/rpl/fail.h
+++ b/Telegram/SourceFiles/rpl/fail.h
@@ -26,10 +26,9 @@ namespace rpl {
 
 template <typename Value, typename Error>
 inline auto fail(Error &&error) {
-	using consumer_t = consumer<Value, std::decay_t<Error>>;
 	return make_producer<Value, std::decay_t<Error>>([
 		error = std::forward<Error>(error)
-	](const consumer_t &consumer) mutable {
+	](const auto &consumer) mutable {
 		consumer.put_error(std::move(error));
 		return lifetime();
 	});
diff --git a/Telegram/SourceFiles/rpl/filter.h b/Telegram/SourceFiles/rpl/filter.h
index bbff03f9dd..fe2ea1fb06 100644
--- a/Telegram/SourceFiles/rpl/filter.h
+++ b/Telegram/SourceFiles/rpl/filter.h
@@ -43,11 +43,10 @@ public:
 		typename = std::enable_if_t<
 			details::is_callable_v<Predicate, Value>>>
 	auto operator()(producer<Value, Error, Generator> &&initial) {
-		using consumer_type = consumer<Value, Error>;
 		return make_producer<Value, Error>([
 			initial = std::move(initial),
 			predicate = std::move(_predicate)
-		](const consumer_type &consumer) mutable {
+		](const auto &consumer) mutable {
 			return std::move(initial).start(
 				[
 					consumer,
@@ -126,10 +125,9 @@ public:
 			base::optional<Value>,
 			Error,
 			Generator> &&initial) const {
-		using consumer_type = consumer<Value, Error>;
 		return make_producer<Value, Error>([
 			initial = std::move(initial)
-		](const consumer_type &consumer) mutable {
+		](const auto &consumer) mutable {
 			return std::move(initial).start(
 				[consumer](auto &&value) {
 					if (value) {
diff --git a/Telegram/SourceFiles/rpl/flatten_latest.h b/Telegram/SourceFiles/rpl/flatten_latest.h
index 5a882d4fde..921124f454 100644
--- a/Telegram/SourceFiles/rpl/flatten_latest.h
+++ b/Telegram/SourceFiles/rpl/flatten_latest.h
@@ -36,10 +36,9 @@ public:
 			producer<Value, Error, Generator>,
 			Error,
 			MetaGenerator> &&initial) const {
-		using consumer_type = consumer<Value, Error>;
 		return make_producer<Value, Error>([
 			initial = std::move(initial)
-		](const consumer_type &consumer) mutable {
+		](const auto &consumer) mutable {
 			auto state = std::make_shared<State>();
 			return std::move(initial).start(
 			[consumer, state](producer<Value, Error> &&inner) {
diff --git a/Telegram/SourceFiles/rpl/map.h b/Telegram/SourceFiles/rpl/map.h
index 644e096550..9158726eea 100644
--- a/Telegram/SourceFiles/rpl/map.h
+++ b/Telegram/SourceFiles/rpl/map.h
@@ -28,12 +28,13 @@ namespace details {
 template <
 	typename Transform,
 	typename NewValue,
-	typename Error>
+	typename Error,
+	typename Handlers>
 class map_transform_helper {
 public:
 	map_transform_helper(
 		Transform &&transform,
-		const consumer<NewValue, Error> &consumer)
+		const consumer<NewValue, Error, Handlers> &consumer)
 		: _consumer(consumer)
 		, _transform(std::move(transform)) {
 	}
@@ -55,7 +56,7 @@ public:
 	}
 
 private:
-	consumer<NewValue, Error> _consumer;
+	consumer<NewValue, Error, Handlers> _consumer;
 	Transform _transform;
 
 };
@@ -64,12 +65,13 @@ template <
 	typename Transform,
 	typename NewValue,
 	typename Error,
+	typename Handlers,
 	typename = std::enable_if_t<
 		std::is_rvalue_reference_v<Transform&&>>>
-inline map_transform_helper<Transform, NewValue, Error>
+inline map_transform_helper<Transform, NewValue, Error, Handlers>
 map_transform(
 		Transform &&transform,
-		const consumer<NewValue, Error> &consumer) {
+		const consumer<NewValue, Error, Handlers> &consumer) {
 	return { std::move(transform), consumer };
 }
 
@@ -92,7 +94,7 @@ public:
 		return make_producer<NewValue, Error>([
 			initial = std::move(initial),
 			transform = std::move(_transform)
-		](const consumer<NewValue, Error> &consumer) mutable {
+		](const auto &consumer) mutable {
 			return std::move(initial).start(
 			map_transform(
 				std::move(transform),
@@ -125,12 +127,13 @@ namespace details {
 template <
 	typename Transform,
 	typename Value,
-	typename NewError>
+	typename NewError,
+	typename Handlers>
 class map_error_transform_helper {
 public:
 	map_error_transform_helper(
 		Transform &&transform,
-		const consumer<Value, NewError> &consumer)
+		const consumer<Value, NewError, Handlers> &consumer)
 		: _transform(std::move(transform))
 		, _consumer(consumer) {
 	}
@@ -152,7 +155,7 @@ public:
 	}
 
 private:
-	consumer<Value, NewError> _consumer;
+	consumer<Value, NewError, Handlers> _consumer;
 	Transform _transform;
 
 };
@@ -161,12 +164,13 @@ template <
 	typename Transform,
 	typename Value,
 	typename NewError,
+	typename Handlers,
 	typename = std::enable_if_t<
 		std::is_rvalue_reference_v<Transform&&>>>
-inline map_error_transform_helper<Transform, Value, NewError>
+inline map_error_transform_helper<Transform, Value, NewError, Handlers>
 map_error_transform(
 		Transform &&transform,
-		const consumer<Value, NewError> &consumer) {
+		const consumer<Value, NewError, Handlers> &consumer) {
 	return { std::move(transform), consumer };
 }
 
@@ -189,7 +193,7 @@ public:
 		return make_producer<Value, NewError>([
 			initial = std::move(initial),
 			transform = std::move(_transform)
-		](const consumer<Value, NewError> &consumer) mutable {
+		](const auto &consumer) mutable {
 			return std::move(initial).start(
 			[consumer](auto &&value) {
 				consumer.put_next_forward(
diff --git a/Telegram/SourceFiles/rpl/never.h b/Telegram/SourceFiles/rpl/never.h
index f9091355fb..cc42198465 100644
--- a/Telegram/SourceFiles/rpl/never.h
+++ b/Telegram/SourceFiles/rpl/never.h
@@ -26,9 +26,7 @@ namespace rpl {
 
 template <typename Value = empty_value, typename Error = no_error>
 inline auto never() {
-	using consumer_type = consumer<Value, Error>;
-	return make_producer<Value, Error>([](
-			const consumer_type &consumer) {
+	return make_producer<Value, Error>([](const auto &consumer) {
 		return lifetime();
 	});
 }
diff --git a/Telegram/SourceFiles/rpl/producer.h b/Telegram/SourceFiles/rpl/producer.h
index 9248d82d90..a70c74eb25 100644
--- a/Telegram/SourceFiles/rpl/producer.h
+++ b/Telegram/SourceFiles/rpl/producer.h
@@ -60,9 +60,10 @@ private:
 template <typename Value, typename Error>
 class type_erased_generator final {
 public:
+	template <typename Handlers>
+	using consumer_type = consumer<Value, Error, Handlers>;
 	using value_type = Value;
 	using error_type = Error;
-	using consumer_type = consumer<Value, Error>;
 
 	type_erased_generator(
 		const type_erased_generator &other) = default;
@@ -102,12 +103,13 @@ public:
 		return *this;
 	}
 
-	lifetime operator()(const consumer_type &consumer) {
+	template <typename Handlers>
+	lifetime operator()(const consumer_type<Handlers> &consumer) {
 		return _implementation(consumer);
 	}
 
 private:
-	base::lambda<lifetime(const consumer_type &)> _implementation;
+	base::lambda<lifetime(const consumer_type<type_erased_handlers<Value, Error>> &)> _implementation;
 
 };
 
@@ -162,9 +164,10 @@ namespace details {
 template <typename Value, typename Error, typename Generator>
 class producer_base {
 public:
+	template <typename Handlers>
+	using consumer_type = consumer<Value, Error, Handlers>;
 	using value_type = Value;
 	using error_type = Error;
-	using consumer_type = consumer<Value, Error>;
 
 	template <
 		typename OtherGenerator,
@@ -203,7 +206,9 @@ public:
 		OnError &&error,
 		OnDone &&done) const &;
 
-	lifetime start_existing(const consumer_type &consumer) &&;
+	template <typename Handlers>
+	lifetime start_existing(
+		const consumer_type<Handlers> &consumer) &&;
 
 private:
 	Generator _generator;
@@ -233,7 +238,7 @@ inline lifetime producer_base<Value, Error, Generator>::start(
 		OnNext &&next,
 		OnError &&error,
 		OnDone &&done) && {
-	return std::move(*this).start_existing(consumer<Value, Error>(
+	return std::move(*this).start_existing(make_consumer<Value, Error>(
 		std::forward<OnNext>(next),
 		std::forward<OnError>(error),
 		std::forward<OnDone>(done)));
@@ -257,8 +262,9 @@ inline lifetime producer_base<Value, Error, Generator>::start_copy(
 }
 
 template <typename Value, typename Error, typename Generator>
+template <typename Handlers>
 inline lifetime producer_base<Value, Error, Generator>::start_existing(
-		const consumer_type &consumer) && {
+		const consumer_type<Handlers> &consumer) && {
 	consumer.add_lifetime(std::move(_generator)(consumer));
 	return [consumer] { consumer.terminate(); };
 }
@@ -278,6 +284,7 @@ class producer final
 		Value,
 		Error,
 		Generator>;
+
 public:
 	using parent_type::parent_type;
 
@@ -292,6 +299,7 @@ class producer<
 	using parent_type = details::producer_base_type_erased<
 		Value,
 		Error>;
+
 public:
 	using parent_type::parent_type;;
 
diff --git a/Telegram/SourceFiles/rpl/range.h b/Telegram/SourceFiles/rpl/range.h
index 6f5cc5a4a9..da6026c915 100644
--- a/Telegram/SourceFiles/rpl/range.h
+++ b/Telegram/SourceFiles/rpl/range.h
@@ -26,10 +26,9 @@ namespace rpl {
 
 template <typename Value>
 inline auto single(Value &&value) {
-	using consumer_type = consumer<std::decay_t<Value>, no_error>;
 	return make_producer<std::decay_t<Value>>([
 		value = std::forward<Value>(value)
-	](const consumer_type &consumer) mutable {
+	](const auto &consumer) mutable {
 		consumer.put_next(std::move(value));
 		consumer.put_done();
 		return lifetime();
@@ -37,9 +36,7 @@ inline auto single(Value &&value) {
 }
 
 inline auto single() {
-	using consumer_type = consumer<empty_value, no_error>;
-	return make_producer<>([](
-			const consumer_type &consumer) {
+	return make_producer<>([](const auto &consumer) {
 		consumer.put_next({});
 		consumer.put_done();
 		return lifetime();
@@ -48,10 +45,9 @@ inline auto single() {
 
 template <typename Value>
 inline auto vector(std::vector<Value> &&values) {
-	using consumer_type = consumer<Value, no_error>;
 	return make_producer<Value>([
 		values = std::move(values)
-	](const consumer_type &consumer) mutable {
+	](const auto &consumer) mutable {
 		for (auto &value : values) {
 			consumer.put_next(std::move(value));
 		}
@@ -61,10 +57,9 @@ inline auto vector(std::vector<Value> &&values) {
 }
 
 inline auto vector(std::vector<bool> &&values) {
-	using consumer_type = consumer<bool, no_error>;
 	return make_producer<bool>([
 		values = std::move(values)
-	](const consumer_type &consumer) {
+	](const auto &consumer) {
 		for (auto value : values) {
 			consumer.put_next_copy(value);
 		}
@@ -85,8 +80,7 @@ inline auto range(Range &&range) {
 
 inline auto ints(int from, int till) {
 	Expects(from <= till);
-	return make_producer<int>([from, till](
-			const consumer<int> &consumer) {
+	return make_producer<int>([from, till](const auto &consumer) {
 		for (auto i = from; i != till; ++i) {
 			consumer.put_next_copy(i);
 		}
diff --git a/Telegram/SourceFiles/rpl/then.h b/Telegram/SourceFiles/rpl/then.h
index c066c906b8..91d3dbb506 100644
--- a/Telegram/SourceFiles/rpl/then.h
+++ b/Telegram/SourceFiles/rpl/then.h
@@ -41,11 +41,10 @@ public:
 	auto operator()(
 		producer<OtherValue, OtherError, OtherGenerator> &&initial
 	) {
-		using consumer_type = consumer<NewValue, NewError>;
 		return make_producer<NewValue, NewError>([
 			initial = std::move(initial),
 			following = std::move(_following)
-		](const consumer_type &consumer) mutable {
+		](const auto &consumer) mutable {
 			return std::move(initial).start(
 			[consumer](auto &&value) {
 				consumer.put_next_forward(