The copy constructor for weak_ptr constructs px like so:

Why do it this way and not just:

This introduces a somewhat unexpected race in that the shared_ptr obtained with lock() can be the last outstanding shared_ptr and the object can be destroyed during this copy. It is certainly not a bug in the smart_ptr library, but the behavior is unexpected and quite inconvenient. I assume there is a reason for calling lock() and not just copying the pointer and I would like to know what it is.

Thanks,

Travis Gockel