diff --git a/Telegram/SourceFiles/app.cpp b/Telegram/SourceFiles/app.cpp
index 131816012..2a8997e12 100644
--- a/Telegram/SourceFiles/app.cpp
+++ b/Telegram/SourceFiles/app.cpp
@@ -208,7 +208,11 @@ namespace {
 
 	void logOut() {
 		if (auto mtproto = Messenger::Instance().mtp()) {
-			mtproto->logout(rpcDone(&loggedOut), rpcFail(&loggedOut));
+			mtproto->logout(rpcDone([] {
+				return loggedOut();
+			}), rpcFail([] {
+				return loggedOut();
+			}));
 		} else {
 			// We log out because we've forgotten passcode.
 			// So we just start mtproto from scratch.
diff --git a/Telegram/SourceFiles/base/lambda.h b/Telegram/SourceFiles/base/lambda.h
index 6046bff58..266a1cdf5 100644
--- a/Telegram/SourceFiles/base/lambda.h
+++ b/Telegram/SourceFiles/base/lambda.h
@@ -22,6 +22,36 @@ Copyright (c) 2014-2017 John Preston, https://desktop.telegram.org
 
 #include <memory>
 
+#ifndef CUSTOM_LAMBDA_WRAP
+
+#include <functional>
+#include "base/unique_function.h"
+
+namespace base {
+
+template <typename Function>
+using lambda = std::function<Function>;
+
+template <typename Function>
+using lambda_once = unique_function<Function>;
+
+namespace lambda_internal {
+
+template <typename Lambda>
+struct lambda_call_type {
+	using type = decltype(&Lambda::operator());
+};
+
+} // namespace lambda_internal
+
+template <typename Lambda>
+using lambda_call_type_t
+	= typename lambda_internal::lambda_call_type<Lambda>::type;
+
+} // namespace base
+
+#else // CUSTOM_LAMBDA_WRAP
+
 #ifndef Assert
 #define LambdaAssertDefined
 #define Assert(v) ((v) ? ((void)0) : std::abort())
@@ -67,9 +97,6 @@ struct type_helper {
 template <typename Lambda>
 using lambda_type = typename lambda_internal::type_helper<std::decay_t<Lambda>>::type;
 
-template <typename Lambda>
-constexpr bool lambda_is_mutable = lambda_internal::type_helper<std::decay_t<Lambda>>::is_mutable;
-
 namespace lambda_internal {
 
 constexpr auto kFullStorageSize = 32U;
@@ -469,3 +496,5 @@ public:
 #ifdef LambdaUnexpectedDefined
 #undef Unexpected
 #endif // LambdaUnexpectedDefined
+
+#endif // CUSTOM_LAMBDA_WRAP
diff --git a/Telegram/SourceFiles/base/lambda_guard.h b/Telegram/SourceFiles/base/lambda_guard.h
index c68825d3c..735dfe486 100644
--- a/Telegram/SourceFiles/base/lambda_guard.h
+++ b/Telegram/SourceFiles/base/lambda_guard.h
@@ -31,8 +31,6 @@ namespace lambda_internal {
 template <int N, typename Lambda>
 class guard_data {
 public:
-	using return_type = typename lambda_type<Lambda>::return_type;
-
 	template <typename ...PointersAndLambda>
 	inline guard_data(PointersAndLambda&&... qobjectsAndLambda) : _lambda(init(_pointers, std::forward<PointersAndLambda>(qobjectsAndLambda)...)) {
 	}
@@ -43,8 +41,10 @@ public:
 		}
 	}
 
-	template <typename ...Args>
-	inline return_type operator()(Args&&... args) {
+	template <
+		typename ...Args,
+		typename return_type = decltype(std::declval<Lambda>()(std::declval<Args>()...))>
+	inline auto operator()(Args&&... args) {
 		for (int i = 0; i != N; ++i) {
 			if (!_pointers[i]) {
 				return return_type();
@@ -53,8 +53,10 @@ public:
 		return _lambda(std::forward<Args>(args)...);
 	}
 
-	template <typename ...Args>
-	inline return_type operator()(Args&&... args) const {
+	template <
+		typename ...Args,
+		typename return_type = decltype(std::declval<Lambda>()(std::declval<Args>()...))>
+	inline auto operator()(Args&&... args) const {
 		for (int i = 0; i != N; ++i) {
 			if (!_pointers[i]) {
 				return return_type();
@@ -74,15 +76,18 @@ private:
 	}
 
 	QPointer<QObject> _pointers[N];
-	Lambda _lambda;
+	mutable Lambda _lambda;
 
 };
 
+template <int N, typename Lambda>
+struct lambda_call_type<guard_data<N, Lambda>> {
+	using type = lambda_call_type_t<Lambda>;
+};
+
 template <int N, typename Lambda>
 class guard {
 public:
-	using return_type = typename lambda_type<Lambda>::return_type;
-
 	template <typename Pointer, typename Other, typename ...PointersAndLambda>
 	inline guard(Pointer &&qobject, Other &&other, PointersAndLambda&&... qobjectsAndLambda) : _data(std::make_unique<guard_data<N, Lambda>>(std::forward<Pointer>(qobject), std::forward<Other>(other), std::forward<PointersAndLambda>(qobjectsAndLambda)...)) {
 		static_assert(1 + 1 + sizeof...(PointersAndLambda) == N + 1, "Wrong argument count!");
@@ -104,13 +109,17 @@ public:
 		return *this;
 	}
 
-	template <typename ...Args>
-	inline return_type operator()(Args&&... args) {
+	template <
+		typename ...Args,
+		typename = decltype(std::declval<Lambda>()(std::declval<Args>()...))>
+	inline decltype(auto) operator()(Args&&... args) {
 		return (*_data)(std::forward<Args>(args)...);
 	}
 
-	template <typename ...Args>
-	inline return_type operator()(Args&&... args) const {
+	template <
+		typename ...Args,
+		typename = decltype(std::declval<Lambda>()(std::declval<Args>()...))>
+	inline decltype(auto) operator()(Args&&... args) const {
 		return (*_data)(std::forward<Args>(args)...);
 	}
 
@@ -123,6 +132,11 @@ private:
 
 };
 
+template <int N, typename Lambda>
+struct lambda_call_type<guard<N, Lambda>> {
+	using type = lambda_call_type_t<Lambda>;
+};
+
 template <int N, int K, typename ...PointersAndLambda>
 struct guard_type;
 
@@ -133,7 +147,7 @@ struct guard_type<N, K, Pointer, PointersAndLambda...> {
 
 template <int N, typename Lambda>
 struct guard_type<N, 0, Lambda> {
-	using type = guard<N, Lambda>;
+	using type = guard<N, std::decay_t<Lambda>>;
 };
 
 template <typename ...PointersAndLambda>
@@ -145,12 +159,6 @@ struct guard_type_helper {
 template <typename ...PointersAndLambda>
 using guard_t = typename guard_type_helper<PointersAndLambda...>::type;
 
-template <int N, typename Lambda>
-struct type_helper<guard<N, Lambda>> {
-	using type = typename type_helper<Lambda>::type;
-	static constexpr auto is_mutable = type_helper<Lambda>::is_mutable;
-};
-
 } // namespace lambda_internal
 
 template <typename ...PointersAndLambda>
diff --git a/Telegram/SourceFiles/base/unique_function.h b/Telegram/SourceFiles/base/unique_function.h
new file mode 100644
index 000000000..1bcfe171f
--- /dev/null
+++ b/Telegram/SourceFiles/base/unique_function.h
@@ -0,0 +1,190 @@
+/*
+This file is part of Telegram Desktop,
+the official desktop version of Telegram messaging app, see https://telegram.org
+
+Telegram Desktop is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+It is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+GNU General Public License for more details.
+
+In addition, as a special exception, the copyright holders give permission
+to link the code of portions of this program with the OpenSSL library.
+
+Full license: https://github.com/telegramdesktop/tdesktop/blob/master/LICENSE
+Copyright (c) 2014-2017 John Preston, https://desktop.telegram.org
+*/
+#pragma once
+
+#ifndef Unexpected
+#define Unexpected(message) std::abort()
+#define UniqueFunctionUnexpected
+#endif // Unexpected
+
+namespace base {
+namespace details {
+
+template <typename Callable>
+class moveable_callable_wrap {
+public:
+	static_assert(
+		std::is_move_constructible_v<Callable>,
+		"Should be at least moveable.");
+
+	moveable_callable_wrap(Callable &&other)
+	: _value(std::move(other)) {
+	}
+	moveable_callable_wrap &operator=(Callable &&other) {
+		_value = std::move(other);
+		return *this;
+	}
+	moveable_callable_wrap(moveable_callable_wrap &&other)
+	: _value(std::move(other._value)) {
+	}
+	moveable_callable_wrap(
+			const moveable_callable_wrap &other)
+	: _value(fail_construct()) {
+	}
+	moveable_callable_wrap &operator=(
+			moveable_callable_wrap &&other) {
+		_value = std::move(other._value);
+		return *this;
+	}
+	moveable_callable_wrap &operator=(
+			const moveable_callable_wrap &other) {
+		return fail_assign();
+	}
+
+	template <typename ...Args>
+	decltype(auto) operator()(Args &&...args) const {
+		return _value(std::forward<Args>(args)...);
+	}
+
+private:
+	[[noreturn]] Callable fail_construct() {
+		Unexpected("Attempt to copy-construct a move-only type.");
+	}
+	[[noreturn]] moveable_callable_wrap &fail_assign() {
+		Unexpected("Attempt to copy-assign a move-only type.");
+	}
+
+	mutable Callable _value;
+
+};
+
+} // namespace details
+
+template <typename Function>
+class unique_function;
+
+template <typename Return, typename ...Args>
+class unique_function<Return(Args...)> final {
+public:
+	unique_function(std::nullptr_t = nullptr) noexcept {
+	}
+	unique_function(const unique_function &other) = delete;
+	unique_function &operator=(const unique_function &other) = delete;
+
+	// Move construct / assign from the same type.
+	unique_function(unique_function &&other)
+	: _impl(std::move(other._impl)) {
+	}
+	unique_function &operator=(unique_function &&other) {
+		_impl = std::move(other._impl);
+		return *this;
+	}
+
+	template <
+		typename Callable,
+		typename = std::enable_if_t<
+			std::is_convertible_v<
+				decltype(std::declval<Callable>()(
+					std::declval<Args>()...)),
+				Return>>>
+	unique_function(Callable &&other)
+	: unique_function(
+		std::forward<Callable>(other),
+		std::is_copy_constructible<std::decay_t<Callable>>{}) {
+	}
+
+	template <
+		typename Callable,
+		typename = std::enable_if_t<
+			std::is_convertible_v<
+				decltype(std::declval<Callable>()(
+					std::declval<Args>()...)),
+				Return>>>
+	unique_function &operator=(Callable &&other) {
+		using Decayed = std::decay_t<Callable>;
+		if constexpr (std::is_copy_constructible_v<Decayed>) {
+			_impl = std::forward<Callable>(other);
+		} else if constexpr (std::is_move_constructible_v<Decayed>) {
+			_impl = details::moveable_callable_wrap<Decayed>(
+				std::forward<Callable>(other));
+		} else {
+			static_assert(false_t(other), "Should be moveable.");
+		}
+		return *this;
+	}
+
+	void swap(unique_function &other) {
+		_impl.swap(other._impl);
+	}
+
+	template <typename ...OtherArgs>
+	Return operator()(OtherArgs &&...args) {
+		return _impl(std::forward<OtherArgs>(args)...);
+	}
+
+	explicit operator bool() const {
+		return _impl.operator bool();
+	}
+
+	friend inline bool operator==(
+			const unique_function &value,
+			std::nullptr_t) noexcept {
+		return value._impl == nullptr;
+	}
+	friend inline bool operator==(
+			std::nullptr_t,
+			const unique_function &value) noexcept {
+		return value._impl == nullptr;
+	}
+	friend inline bool operator!=(
+			const unique_function &value,
+			std::nullptr_t) noexcept {
+		return value._impl != nullptr;
+	}
+	friend inline bool operator!=(
+			std::nullptr_t,
+			const unique_function &value) noexcept {
+		return value._impl != nullptr;
+	}
+
+private:
+	template <typename Callable>
+	unique_function(Callable &&other, std::true_type)
+	: _impl(std::forward<Callable>(other)) {
+	}
+
+	template <typename Callable>
+	unique_function(Callable &&other, std::false_type)
+	: _impl(details::moveable_callable_wrap<std::decay_t<Callable>>(
+		std::forward<Callable>(other))) {
+	}
+
+	std::function<Return(Args...)> _impl;
+
+};
+
+} // namespace base
+
+#ifdef UniqueFunctionUnexpected
+#undef UniqueFunctionUnexpected
+#undef Unexpected
+#endif // UniqueFunctionUnexpectedb
+
diff --git a/Telegram/SourceFiles/mtproto/rpc_sender.h b/Telegram/SourceFiles/mtproto/rpc_sender.h
index aa914baa1..a6e7a6ff2 100644
--- a/Telegram/SourceFiles/mtproto/rpc_sender.h
+++ b/Telegram/SourceFiles/mtproto/rpc_sender.h
@@ -20,6 +20,8 @@ Copyright (c) 2014-2017 John Preston, https://desktop.telegram.org
 */
 #pragma once
 
+#include <rpl/details/callable.h>
+
 class RPCError {
 public:
 	RPCError(const MTPrpcError &error) : _code(error.c_rpc_error().verror_code.v) {
@@ -921,7 +923,9 @@ class RPCDoneHandlerImplementationNo : public RPCDoneHandlerImplementation<R()>
 public:
 	using RPCDoneHandlerImplementation<R()>::Parent::Parent;
 	void operator()(mtpRequestId requestId, const mtpPrime *from, const mtpPrime *end) override {
-		return this->_handler ? this->_handler() : void(0);
+		if (this->_handler) {
+			this->_handler();
+		}
 	}
 
 };
@@ -931,44 +935,101 @@ class RPCDoneHandlerImplementationNoReq : public RPCDoneHandlerImplementation<R(
 public:
 	using RPCDoneHandlerImplementation<R(mtpRequestId)>::Parent::Parent;
 	void operator()(mtpRequestId requestId, const mtpPrime *from, const mtpPrime *end) override {
-		return this->_handler ? this->_handler(requestId) : void(0);
+		if (this->_handler) {
+			this->_handler(requestId);
+		}
 	}
 
 };
 
-template <typename R>
-inline RPCDoneHandlerPtr rpcDone_lambda_wrap_helper(base::lambda_once<R(const mtpPrime*, const mtpPrime*)> lambda) {
-	return RPCDoneHandlerPtr(new RPCDoneHandlerImplementationBare<R>(std::move(lambda)));
-}
-
-template <typename R>
-inline RPCDoneHandlerPtr rpcDone_lambda_wrap_helper(base::lambda_once<R(const mtpPrime*, const mtpPrime*, mtpRequestId)> lambda) {
-	return RPCDoneHandlerPtr(new RPCDoneHandlerImplementationBareReq<R>(std::move(lambda)));
-}
-
-template <typename R, typename T>
-inline RPCDoneHandlerPtr rpcDone_lambda_wrap_helper(base::lambda_once<R(const T&)> lambda) {
-	return RPCDoneHandlerPtr(new RPCDoneHandlerImplementationPlain<R, T>(std::move(lambda)));
-}
-
-template <typename R, typename T>
-inline RPCDoneHandlerPtr rpcDone_lambda_wrap_helper(base::lambda_once<R(const T&, mtpRequestId)> lambda) {
-	return RPCDoneHandlerPtr(new RPCDoneHandlerImplementationReq<R, T>(std::move(lambda)));
-}
-
-template <typename R>
-inline RPCDoneHandlerPtr rpcDone_lambda_wrap_helper(base::lambda_once<R()> lambda) {
-	return RPCDoneHandlerPtr(new RPCDoneHandlerImplementationNo<R>(std::move(lambda)));
-}
-
-template <typename R>
-inline RPCDoneHandlerPtr rpcDone_lambda_wrap_helper(base::lambda_once<R(mtpRequestId)> lambda) {
-	return RPCDoneHandlerPtr(new RPCDoneHandlerImplementationNoReq<R>(std::move(lambda)));
-}
+template <typename Lambda>
+constexpr bool rpcDone_canCallBare_v = rpl::details::is_callable_plain_v<
+	Lambda, const mtpPrime*, const mtpPrime*>;
 
 template <typename Lambda>
+constexpr bool rpcDone_canCallBareReq_v = rpl::details::is_callable_plain_v<
+	Lambda, const mtpPrime*, const mtpPrime*, mtpRequestId>;
+
+template <typename Lambda>
+constexpr bool rpcDone_canCallNo_v = rpl::details::is_callable_plain_v<
+	Lambda>;
+
+template <typename Lambda>
+constexpr bool rpcDone_canCallNoReq_v = rpl::details::is_callable_plain_v<
+	Lambda, mtpRequestId>;
+
+template <typename Function>
+struct rpcDone_canCallPlain : std::false_type {
+};
+
+template <typename Lambda, typename Return, typename T>
+struct rpcDone_canCallPlain<Return(Lambda::*)(const T&)> : std::true_type {
+	using Arg = T;
+};
+
+template <typename Lambda, typename Return, typename T>
+struct rpcDone_canCallPlain<Return(Lambda::*)(const T&)const>
+	: rpcDone_canCallPlain<Return(Lambda::*)(const T&)> {
+};
+
+template <typename Function>
+constexpr bool rpcDone_canCallPlain_v = rpcDone_canCallPlain<Function>::value;
+
+template <typename Function>
+struct rpcDone_canCallReq : std::false_type {
+};
+
+template <typename Lambda, typename Return, typename T>
+struct rpcDone_canCallReq<Return(Lambda::*)(const T&, mtpRequestId)> : std::true_type {
+	using Arg = T;
+};
+
+template <typename Lambda, typename Return, typename T>
+struct rpcDone_canCallReq<Return(Lambda::*)(const T&, mtpRequestId)const>
+	: rpcDone_canCallReq<Return(Lambda::*)(const T&, mtpRequestId)> {
+};
+
+template <typename Function>
+constexpr bool rpcDone_canCallReq_v = rpcDone_canCallReq<Function>::value;
+
+template <typename Function>
+struct rpcDone_returnType;
+
+template <typename Lambda, typename Return, typename ...Args>
+struct rpcDone_returnType<Return(Lambda::*)(Args...)> {
+	using type = Return;
+};
+
+template <typename Lambda, typename Return, typename ...Args>
+struct rpcDone_returnType<Return(Lambda::*)(Args...)const> {
+	using type = Return;
+};
+
+template <typename Function>
+using rpcDone_returnType_t = typename rpcDone_returnType<Function>::type;
+
+template <
+	typename Lambda,
+	typename Function = base::lambda_call_type_t<Lambda>>
 RPCDoneHandlerPtr rpcDone(Lambda lambda) {
-	return rpcDone_lambda_wrap_helper(base::lambda_type<Lambda>(std::move(lambda)));
+	using R = rpcDone_returnType_t<Function>;
+	if constexpr (rpcDone_canCallBare_v<Lambda>) {
+		return RPCDoneHandlerPtr(new RPCDoneHandlerImplementationBare<R>(std::move(lambda)));
+	} else if constexpr (rpcDone_canCallBareReq_v<Lambda>) {
+		return RPCDoneHandlerPtr(new RPCDoneHandlerImplementationBareReq<R>(std::move(lambda)));
+	} else if constexpr (rpcDone_canCallNo_v<Lambda>) {
+		return RPCDoneHandlerPtr(new RPCDoneHandlerImplementationNo<R>(std::move(lambda)));
+	} else if constexpr (rpcDone_canCallNoReq_v<Lambda>) {
+		return RPCDoneHandlerPtr(new RPCDoneHandlerImplementationNoReq<R>(std::move(lambda)));
+	} else if constexpr (rpcDone_canCallPlain_v<Function>) {
+		using T = typename rpcDone_canCallPlain<Function>::Arg;
+		return RPCDoneHandlerPtr(new RPCDoneHandlerImplementationPlain<R, T>(std::move(lambda)));
+	} else if constexpr (rpcDone_canCallReq_v<Function>) {
+		using T = typename rpcDone_canCallReq<Function>::Arg;
+		return RPCDoneHandlerPtr(new RPCDoneHandlerImplementationReq<R, T>(std::move(lambda)));
+	} else {
+		static_assert(false_t(lambda), "Unknown method.");
+	}
 }
 
 template <typename FunctionType>
@@ -1010,23 +1071,35 @@ public:
 
 };
 
-inline RPCFailHandlerPtr rpcFail_lambda_wrap_helper(base::lambda_once<bool(const RPCError&)> lambda) {
-	return RPCFailHandlerPtr(new RPCFailHandlerImplementationPlain(std::move(lambda)));
-}
-
-inline RPCFailHandlerPtr rpcFail_lambda_wrap_helper(base::lambda_once<bool(const RPCError&, mtpRequestId)> lambda) {
-	return RPCFailHandlerPtr(new RPCFailHandlerImplementationReq(std::move(lambda)));
-}
-
-inline RPCFailHandlerPtr rpcFail_lambda_wrap_helper(base::lambda_once<bool()> lambda) {
-	return RPCFailHandlerPtr(new RPCFailHandlerImplementationNo(std::move(lambda)));
-}
-
-inline RPCFailHandlerPtr rpcFail_lambda_wrap_helper(base::lambda_once<bool(mtpRequestId)> lambda) {
-	return RPCFailHandlerPtr(new RPCFailHandlerImplementationNoReq(std::move(lambda)));
-}
+template <typename Lambda>
+constexpr bool rpcFail_canCallNo_v = rpl::details::is_callable_plain_v<
+	Lambda>;
 
 template <typename Lambda>
+constexpr bool rpcFail_canCallNoReq_v = rpl::details::is_callable_plain_v<
+	Lambda, mtpRequestId>;
+
+template <typename Lambda>
+constexpr bool rpcFail_canCallPlain_v = rpl::details::is_callable_plain_v<
+	Lambda, const RPCError&>;
+
+template <typename Lambda>
+constexpr bool rpcFail_canCallReq_v = rpl::details::is_callable_plain_v<
+	Lambda, const RPCError&, mtpRequestId>;
+
+template <
+	typename Lambda,
+	typename Function = base::lambda_call_type_t<Lambda>>
 RPCFailHandlerPtr rpcFail(Lambda lambda) {
-	return rpcFail_lambda_wrap_helper(base::lambda_type<Lambda>(std::move(lambda)));
+	if constexpr (rpcFail_canCallNo_v<Lambda>) {
+		return RPCFailHandlerPtr(new RPCFailHandlerImplementationNo(std::move(lambda)));
+	} else if constexpr (rpcFail_canCallNoReq_v<Lambda>) {
+		return RPCFailHandlerPtr(new RPCFailHandlerImplementationNoReq(std::move(lambda)));
+	} else if constexpr (rpcFail_canCallPlain_v<Lambda>) {
+		return RPCFailHandlerPtr(new RPCFailHandlerImplementationPlain(std::move(lambda)));
+	} else if constexpr (rpcFail_canCallReq_v<Lambda>) {
+		return RPCFailHandlerPtr(new RPCFailHandlerImplementationReq(std::move(lambda)));
+	} else {
+		static_assert(false_t(lambda), "Unknown method.");
+	}
 }
diff --git a/Telegram/gyp/telegram_sources.txt b/Telegram/gyp/telegram_sources.txt
index f43144ab3..8e0eb7de1 100644
--- a/Telegram/gyp/telegram_sources.txt
+++ b/Telegram/gyp/telegram_sources.txt
@@ -27,6 +27,7 @@
 <(src_loc)/base/timer.h
 <(src_loc)/base/type_traits.h
 <(src_loc)/base/unique_any.h
+<(src_loc)/base/unique_function.h
 <(src_loc)/base/variant.h
 <(src_loc)/base/virtual_method.h
 <(src_loc)/base/weak_unique_ptr.h