Re: Smart pointer for observe only behavior

"Daniel T." <>
Thu, 10 Jul 2008 22:40:29 -0400
Soumen <> wrote:

I've requirement to observe a raw pointer (i.e. I should be able to
query if the pointer I'm using is still valid or not but when the
observer goes out of scope, the resource -- memory -- shouldn't be
released). Is there any boost way (or using any other smart
pointer) to achieve this? Since I've a raw pointer, probably I
cannot use weak_ptr.

Is there a way to do this using shared_ptr with custom deleter?

No. You would have to write some sort of observable pointer. I've done
this before but be advised that such a pointer is quite smart and kind
of expensive. You would need two classes, a "master_pointer" that owns
the object in question and "observer_pointers". observer_pointers log
themselves with the master_pointer as holders of pointers to the object
and the master_pointer notifies all the observers when the object is
deleted so they will know the object is no longer valid.

I expect there is a better way to solve your problem though...

OK. The pointer I want to observe say is of class A and class A is
singleton. the creation and destruction of A not managed by
different module (legacy). But my module (new) needs to use some
member functions of A. My module cannot manage A but is dependent
on A. During course of execution, there're chances that A's object
is recreated. And I need to be aware of it. Is there a solution?

Yes and the solution is simple. Don't keep any pointers to the A
singleton. Every time you need to call a member-function on the
singleton object, get the pointer from the A::instance() member-function.

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