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Telegram/SourceFiles/rpl/variable.h

@@ -26,37 +26,24 @@ Copyright (c) 2014-2017 John Preston, https://desktop.telegram.org
 namespace rpl {
 
 template <typename Type>
-class variable {
+class variable final {
 public:
 	variable() : _data{} {
 	}
-	variable(const variable &other) = default;
-	variable(variable &&other) = default;
-	variable &operator=(const variable &other) = default;
-	variable &operator=(variable &&other) = default;
-
-	variable(const Type &data) : _data(data) {
-	}
-	variable(Type &&data) : _data(std::move(data)) {
-	}
-	variable &operator=(const Type &data) {
-		return assign(data);
-	}
 
 	template <
 		typename OtherType,
 		typename = std::enable_if_t<
-			std::is_constructible_v<Type, OtherType&&>
-			&& !std::is_same_v<std::decay_t<OtherType>, Type>>>
+			std::is_constructible_v<Type, OtherType&&>>>
 	variable(OtherType &&data) : _data(std::forward<OtherType>(data)) {
 	}
 
 	template <
 		typename OtherType,
 		typename = std::enable_if_t<
-			std::is_assignable_v<Type, OtherType&&>
-			&& !std::is_same_v<std::decay_t<OtherType>, Type>>>
+			std::is_assignable_v<Type&, OtherType&&>>>
 	variable &operator=(OtherType &&data) {
+		_lifetime.destroy();
 		return assign(std::forward<OtherType>(data));
 	}
 
@@ -65,11 +52,11 @@ public:
 		typename Error,
 		typename Generator,
 		typename = std::enable_if_t<
-			std::is_assignable_v<Type, OtherType>>>
+			std::is_assignable_v<Type&, OtherType>>>
 	variable(producer<OtherType, Error, Generator> &&stream) {
 		std::move(stream)
 			| start_with_next([this](auto &&data) {
-				*this = std::forward<decltype(data)>(data);
+				assign(std::forward<decltype(data)>(data));
 			}, _lifetime);
 	}
 
@@ -78,13 +65,13 @@ public:
 		typename Error,
 		typename Generator,
 		typename = std::enable_if_t<
-			std::is_assignable_v<Type, OtherType>>>
+			std::is_assignable_v<Type&, OtherType>>>
 	variable &operator=(
 			producer<OtherType, Error, Generator> &&stream) {
 		_lifetime.destroy();
 		std::move(stream)
 			| start_with_next([this](auto &&data) {
-				*this = std::forward<decltype(data)>(data);
+				assign(std::forward<decltype(data)>(data));
 			}, _lifetime);
 	}
 
@@ -96,11 +83,39 @@ public:
 	}
 
 private:
+	template <typename A, typename B>
+	struct supports_equality_compare {
+		template <typename U, typename V>
+		static auto test(const U *u, const V *v)
+			-> decltype(*u == *v, details::true_t());
+		static details::false_t test(...);
+		static constexpr bool value
+			= (sizeof(test(
+				(std::decay_t<A>*)nullptr,
+				(std::decay_t<B>*)nullptr
+			)) == sizeof(details::true_t));
+	};
+	template <typename A, typename B>
+	static constexpr bool supports_equality_compare_v
+		= supports_equality_compare<A, B>::value;
+
 	template <typename OtherType>
 	variable &assign(OtherType &&data) {
-		_lifetime.destroy();
-		_data = std::forward<OtherType>(data);
-		_changes.fire_copy(_data);
+		if constexpr (supports_equality_compare_v<Type, OtherType>) {
+			if (!(_data == data)) {
+				_data = std::forward<OtherType>(data);
+				_changes.fire_copy(_data);
+			}
+		} else if constexpr (supports_equality_compare_v<Type, Type>) {
+			auto old = std::move(_data);
+			_data = std::forward<OtherType>(data);
+			if (!(_data == old)) {
+				_changes.fire_copy(_data);
+			}
+		} else {
+			_data = std::forward<OtherType>(data);
+			_changes.fire_copy(_data);
+		}
 		return *this;
 	}
 

Telegram/SourceFiles/rpl/variable_tests.cpp

@@ -0,0 +1,45 @@
+/*
+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
+*/
+#include "catch.hpp"
+
+#include <rpl/rpl.h>
+#include <string>
+
+using namespace rpl;
+
+TEST_CASE("basic variable tests", "[rpl::variable]") {
+	SECTION("simple test") {
+		auto sum = std::make_shared<int>(0);
+		{
+			auto var = variable<int>(1);
+			auto lifeftime = var.value()
+				| start_with_next([=](int value) {
+					*sum += value;
+				});
+			var = 1;
+			var = 11;
+			var = 111;
+			var = 111;
+		}
+		REQUIRE(*sum == 1 + 11 + 111);
+	}
+}
+