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From: Alan Griffiths (alan_at_[hidden])
Date: 1999-08-01 16:12:05

In message <000801bedc3e$fb008170$37781990_at_[hidden]>, Greg Colvin
<gcolvin_at_[hidden]> writes
>Although it seems impossible to create a non-intrusive weak
>pointer class that can track the liveness of an arbitrary class of
>object, it is possible to create one that tracks the liveness of
>objects controlled by shared_ptr.
>The changes to out current shared_ptr would be:
> Switch to the "indirect" implementation of shared_ptr. That
> is, the shared_ptr contains just a pointer to a handle struct
> containing a pointer to the object shared and the count.
> Add a second count field for the number of weak pointers using
> the object. When the number of shared pointers goes to zero
> the shared object is deleted and the pointer to object field is
> zeroed out, but the handle struct is not deleted until both
> counters go to zero.

There is an existing, tested implementation along these lines on my
website (I called the pointers "counted_ptr" and "uncounted_ptr"). If
anyone wants to bring these into boost format and submit them then I
hearby grant permission. (I was hoping to do this myself, but I won't
have time for the foreseeable future.)

There is also a smart pointer that replicates the referenced object on

There is an overview at:

Alan Griffiths  (alan_at_[hidden])
ACCU Chairman   (chair_at_[hidden])   

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