On Fri, Feb 10, 2012 at 2:06 AM, Patrick Mihelich <mihelich@willowgarage.com> wrote:

On Thu, Feb 9, 2012 at 12:55 PM, Dirk Thomas <dthomas@willowgarage.com> wrote:

While I like boost::shared_ptr, it is not always possible to use it nicely.

In rviz I have plugin classes which are subclasses of QWidget (from Qt GUI library). These objects are automatically deleted by Qt when their parent widgets are deleted. I can be notified of their
deletion by Qt, and call an "unload" or "decrement-reference-count" function, but it is not easy to use these QWidget pointers inside boost::shared_ptr without getting double-deletion crashes.

That sounds like a very reasonable use case.
Automatically deleting and unloading is a nice feature but might not always be desired.
Having the option to get a raw pointer (as before) and take care of garbaging stuff manually would be great.

I don't like this, but don't see a clearly better solution.

I actually think you still can use a shared pointer in that case. shared_ptr has a overloaded constructor that takes an explicit delete functor. When the reference count reaches zero, instead of calling delete, the functor is called.

I'm not sure if that helps here, but I think this is at least a possibility to consider. Instead of returning a normal pointer where the user has to calll decrement-reference-count manually, it should be possible to just have a share_ptr deleter that calls the decrement-ref-count function.

Lorenz