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/**
* Copyright (C) 2015 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <boost/static_assert.hpp>
#include <memory>
#include <type_traits>
namespace mongo {
/**
* A "smart" pointer that explicitly indicates a lack of ownership.
* It will implicitly convert from any compatible pointer type except auto_ptr.
*
* Note that like other pointer types const applies to the pointer not the pointee:
* - const unowned_ptr<T> => T* const
* - unowned_ptr<const T> => const T*
*/
template <typename T>
struct unowned_ptr {
unowned_ptr() = default;
//
// Implicit conversions from compatible pointer types
//
// Removes conversions from overload resolution if the underlying pointer types aren't
// convertible. This makes this class behave more like a bare pointer.
template <typename U>
using IfConvertibleFrom = typename std::enable_if<std::is_convertible<U*, T*>::value>::type;
// Needed for NULL since it won't match U* constructor.
unowned_ptr(T* p) : _p(p) {}
template<typename U, typename = IfConvertibleFrom<U>>
unowned_ptr(U* p) : _p(p) {}
template<typename U, typename = IfConvertibleFrom<U>>
unowned_ptr(const unowned_ptr<U>& p) : _p(p) {}
template<typename U, typename = IfConvertibleFrom<U>>
unowned_ptr(const std::unique_ptr<U>& p) : _p(p.get()) {}
template<typename U, typename = IfConvertibleFrom<U>>
unowned_ptr(const std::shared_ptr<U>& p) : _p(p.get()) {}
//
// Modifiers
//
void reset(unowned_ptr p = nullptr) { _p = p.get(); }
void swap(unowned_ptr& other) { std::swap(_p, other._p); }
//
// Accessors
//
T* get() const { return _p; }
operator T*() const { return _p; }
//
// Pointer syntax
//
T* operator->() const { return _p; }
T& operator*() const { return *_p; }
private:
T* _p = nullptr;
};
} // namespace mongo
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