Add base::weak_unique_ptr<T> template class.

Sometimes you don't need shared ownership (shared_ptr), but you
still need to be able to have weak pointers to an object.

Now you can derive the object from base::enable_weak_from_this
and use base::weak_unique_ptr<T> after that.

Telegram/SourceFiles/core/weak_unique_ptr.h

@@ -0,0 +1,88 @@
+/*
+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
+
+namespace base {
+
+class enable_weak_from_this;
+
+template <typename T, typename = std::enable_if_t<std::is_base_of<enable_weak_from_this, T>::value>>
+class weak_unique_ptr;
+
+class enable_weak_from_this {
+public:
+	enable_weak_from_this() = default;
+	enable_weak_from_this(const enable_weak_from_this &other) noexcept {
+	}
+	enable_weak_from_this(enable_weak_from_this &&other) noexcept {
+	}
+	enable_weak_from_this &operator=(const enable_weak_from_this &other) noexcept {
+		return *this;
+	}
+	enable_weak_from_this &operator=(enable_weak_from_this &&other) noexcept {
+		return *this;
+	}
+
+private:
+	template <typename Child, typename>
+	friend class weak_unique_ptr;
+
+	std::shared_ptr<enable_weak_from_this*> getGuarded() {
+		if (!_guarded) {
+			_guarded = std::make_shared<enable_weak_from_this*>(this);
+		}
+		return _guarded;
+	}
+
+	std::shared_ptr<enable_weak_from_this*> _guarded;
+
+};
+
+template <typename T, typename>
+class weak_unique_ptr {
+public:
+	weak_unique_ptr() = default;
+	weak_unique_ptr(T *value) : _guarded(value ? value->getGuarded() : std::shared_ptr<enable_weak_from_this*>()) {
+	}
+	weak_unique_ptr(const std::unique_ptr<T> &value) : _guarded(value ? value->getGuarded() : std::shared_ptr<enable_weak_from_this*>()) {
+	}
+	T *get() const noexcept {
+		if (auto shared = _guarded.lock()) {
+			return static_cast<T*>(*shared);
+		}
+		return nullptr;
+	}
+	explicit operator bool() const noexcept {
+		return !!_guarded.lock();
+	}
+	T &operator*() const noexcept {
+		return *get();
+	}
+	T *operator->() const noexcept {
+		return get();
+	}
+
+private:
+	std::weak_ptr<enable_weak_from_this*> _guarded;
+
+};
+
+} // namespace base

Telegram/gyp/telegram_sources.txt

@@ -87,6 +87,7 @@
 <(src_loc)/core/variant.h
 <(src_loc)/core/version.h
 <(src_loc)/core/virtual_method.h
+<(src_loc)/core/weak_unique_ptr.h
 <(src_loc)/core/zlib_help.h
 <(src_loc)/data/data_abstract_structure.cpp
 <(src_loc)/data/data_abstract_structure.h