[boost] Re: smart_ptr suggestion: Support decrementing shared_ptr'scount,forself-references

From: Chuck Messenger (chuckm_at_[hidden])
Date: 2003-05-27 11:24:26

I take back this suggestion -- intrusive_ptr<> does what I want.

     - Chuck

Chuck Messenger wrote:
> Suppose you have this:
> 
>     struct X {
>         shared_ptr<Y> y;
>         ...
>     };
> 
>     struct Y {
>         X x;
>         ....
>     };
> 
>     struct Z {
>         Z() : pimpl_(new Y()) { pimpl_->x.y = pimpl_; }
>         shared_ptr<Y> pimpl_;
>         ...
>     };
> 
> I'm using the "pimpl" idiom. When I create Z, I create an embedded Y 
> ("y"), setting y's x so that it points to y.
> 
> The problem is that Y will now never die. What I'd like to do is to 
> decrement the reference count in x, when I construct the Y:
> 
>         Z() : pimpl_(new Y()) { pimpl_->x.y = pimpl_;
>                   pimpl_.decrement_reference_count(); }
> 
> This is perfectly sound -- it decrements the reference count from 2 to 
> 1. It says, basically, "the mother structure contains a self-referring 
> pointer. If that's the only one left, then kill the mother structure."
> 
> Why do I want to do all this? Well, I could get into the very sound 
> reasons if anyone is interested. It is a technique for avoiding circular 
> shared_ptr references.
> 
> 
>     - Chuck Messenger
> 
> 
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