[boost] weak_ptr triple states

From: Jaap Suter (boost_at_[hidden])
Date: 2005-07-14 00:21:56

Hi,

a weak_ptr can be said to have three states.

1. Never been assigned to (default constructed)
2. Assigned to, lock will return a shared_ptr to a valid object.
3. Assigned to, but the object pointed to is dead and lock will return null.

As far as I know it is currently impossible to distinguish between case 1 
and 3. Am I overlooking something? If not, can somebody explain the reason 
why it is not possible to distinguish the two cases? Admittedly, I cannot 
come up with any elegant design in which such a distinction is useful, so 
the question is merely theoretical.

Thanks,

Jaap Suter