From: Michael Nicolella (boost_at_[hidden])
Date: 2006-08-18 13:10:42
What if something else has a shared_ptr to B?
-----Original Message-----
From: Scott Meyers [mailto:usenet_at_[hidden]]
Sent: Friday, August 18, 2006 10:05 AM
To: boost-users_at_[hidden]
Subject: [Boost-users] [SmartPointers] weak_ptrs, raw pointers, and cycles
I've recently realized that I just don't get something. Cycles of
shared_ptrs
are bad, because they can lead to resource leaks. To break a cycle, we're
encouraged to use weak_ptrs. Okay, but we could use raw pointers to break
the
cycle, too, and I can't see any advantage offered by the weak_ptr. If A
uses a
shared_ptr to B and B uses a weak_ptr to A, B's life will be shorter than
A's
(its destructor will be invoked from A's destructor and will run to
completion
before A's does), so there is no advantage to a weak_ptr being able to tell
if
it dangles. In this context, it never will. So it seems that using a raw
pointer to break cycles has no disadvantage over a weak_ptr, and it's more
efficient (i.e., smaller and faster). Clearly, I'm missing something. Can
somebody please explain what it is?
I understand that weak_ptrs have other uses (e.g., as observers), so my
question
is only about the advice to use weak_ptrs to break cycles.
Thanks,
Scott
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