Where to delete an object created by factory?

Question

If I have a factory, that creates an object and returns a pointer to it, what will be a better way to delete it:

By delete call in the "user" code, or by a new DestructObject function which I should have together with the factory?

Answer 1

In the general case, the factory might not use plain old new to allocate the object. It may use object and/or page pooling, malloc with placement new, or something even more exotic (memory mapping?). There are at least three ways to handle this that I can think of:

1. Have the factory supply a recycle method to be called when you are done with the object.
2. Return a smart pointer that knows how to do away with the object once no referers remain.
3. Implement a custom delete operator in the object itself.

I hesitate to recommend one over the other, since I haven't given it enough thought in the last five minutes to proffer a definitive opinion, but I would tend to favour the last option in combination with a regular smart pointer like boost/tr1::shared_ptr.

Answer 2

The best way to delete it manually would be not at all.

Answer 3

The following code provides an opportunity not to think about who should remove the newly created object.

class FooFactory
{
public:
    static std::auto_ptr<Foo> CreateInstance();
};

// transmit ownership of created object from factory to 'a' variable
std::auto_ptr<Foo> a = FooFactory::CreateInstance();
// using the created object is not required
FooFactory::CreateInstance();