On Monday 28 April 2008 13:38, Daniel Frey wrote:
I hope it's OK if we discuss it now. So far, I was under the impression that calling shared_from_this() requires that some other shared_ptr takes ownership later. BOOST_ASSERT( _shared_count.empty() ) tests exactly that. It's an easy to understand rule and I can see the use cases.
How would you describe/document the behavior you had in mind? What use case would it serve?
It asserts that no dangling shared_ptrs exist, or that a shared_ptr has taken ownership (in which case it is assumed the user knows what they are doing). It permits, for example, weak_ptrs to exist which might be used to track the object's lifetime whether or not it is actually managed by a shared_ptr. To be more concrete, you might have an object which uses Qt signals/slots and whose lifetime is managed by the Qt framework. You could use shared_from_this() to get a weak_ptr that can be used to track the object's lifetime by thread_safe_signals, for automatic connection management of additional signals/slots from thread_safe_signals. It would work equivalently to boost::trackable from the current boost.signals. On the other hand, I can't think of any situation where aborting on the "no owner and no dangling shared_ptr" case would actually provide any additional safety over allowing it. -- Frank