Jaap Suter wrote:
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.
There is no particular reason to make 1 and 3 indistinguishable. You are right that weak_ptr could have provided an "is empty" query in addition to expired(). There just aren't any compelling use cases for it, as far as I know.