由于具有raii功能,我希望我的对象只能放置在堆栈上,而且作为对象创建的功能也应委派给我不希望ocpy构造函数可用于使用的专业工厂。p>所以我做了这样的事情。
template<typename Product, Args ... >
class Creator : public Product
{
public:
static Product create(Args ... args)
{
return Product(args ... );
}
};
class ProtectedClass
{
ProtectedClass(const ProtectedClass& aThat)=delete;
ProtectedClass& operator=(const ProtectedClass& aThat)=delete;
protected:
ProtectedClass(){}
};
class Spawner
{
public:
ProtectedClass getProtectedClass()
{
return Creator<ProtectedClass>::create();
}
}
int main()
{
Spawner spawner;
//I need protectedClass to be enclosed within this frame
ProtectedClass protectedClass = spawner.getProtectedClass(); // err copy constructor is delted
}
我可以做这样的事情
template<typename Product, Args ... >
class Creator : public Product
{
public:
Creator(Args ... args) : product_(args ...){}
Product& get() const
{
return product_;
}
private:
Product product_;
};
class Spawner
{
public:
std::unique_ptr<Creator<ProtectedClass>> getProtectedClassCreator()
{
return new Creator<ProtectedClass>();
}
}
int main()
{
Spawner spawner;
std::unique_ptr<Creator<ProtectedClass>> creator = std::move(spawner.getProtectedClassCreator());
ProtectedClass& protectedClass = creator->get();
}
,但看起来不正确。
其他方法可以处理?
我这样做的方式将是删除副本,启用移动并允许通过任何可以创建施工密钥的类施工。
// forward declare any factories
class Spawner;
struct ProtectedClass
{
class PermissionKey {
// this is a private constructor
PermissionKey() {};
// make friends of the factories
friend Spawner;
};
// all this is now public.
// because we have declared a constructor, the default constructor
// is deleted.
ProtectedClass(PermissionKey) {}
// disable copies
ProtectedClass(const ProtectedClass& aThat)=delete;
ProtectedClass& operator=(const ProtectedClass& aThat)=delete;
// enable moves so the factory can return it
ProtectedClass(ProtectedClass&& aThat)=default;
ProtectedClass& operator=(ProtectedClass&& aThat)=default;
};
class Spawner
{
public:
ProtectedClass getProtectedClass()
{
// construct our spawned object - we can create keys
return ProtectedClass(ProtectedClass::PermissionKey());
}
};
int main()
{
Spawner spawner;
//I need protectedClass to be enclosed within this frame
auto protectedClass = spawner.getProtectedClass(); // ok now
}