[boost] Re: new approach to smart ptrs -- no new()s is good news

From: Stephen C. Gilardi (squeegee_at_[hidden])
Date: 2000-01-29 08:39:17

>  > if (left == this)
>  >     delete ptr;

I could be wrong, but I don't think this is a correct test for 
uniqueness.  It happens to work in the example test program, but in 
real life these linked pointers can be created and destroyed in any 
order.  It's true that the list always grows by adding elements to 
the right of existing elements, but the elements can be removed in 
any order, including having the leftmost element removed before the 
others.  (Suppose the linked pointer are part of heap-based objects.)

If the only test for uniqueness is "if (left == this)", then when the 
leftmost element is removed, the underlying (pointed to) object is 
deleted.  That's wrong because there may still be other 
linked_pointers pointing to it.

I think the test has to be "if (left == this && right == this)" or 
something equivalent.

--Steve