Re: [boost] Re: how do I release shared_ptr ?

From: Bronek Kozicki (brok_at_[hidden])
Date: 2003-12-29 15:00:48

Jonathan Turkanis <technews_at_[hidden]> wrote:
> This question is addressed directly in the FAQ? (Q. Why doesn't
> shared_ptr provide a release() function? )

lets see FAQ answer:

: A. shared_ptr cannot give away ownership unless it's unique() because
: the other copy will still destroy the object

comment 1. in my real code pointer is always unique, at the point where
I want to initialize auto_ptr from it. Thus (assuming release is added)
it may contain:
 if (!unique())
   throw some_exception();

... and it's OK for me. Of course it means (in context of my previous
sample code) that following:

M m;
m.f();
// ...
std::auto_ptr<int> p = m.source();

... will throw, but:

M m;
// ...
std::auto_ptr<int> p = m.source();

... will work, and this is what I actually need.

comment 2. if shared counter is reset to 0, there's no risk that any
copy of said shared pointer (assuming its non-unique) will try to delete
owned object. There is another risk though: at some point it may own bad
pointer. Overall I think that solution proposed in comment 1. is better.

: Furthermore, the pointer returned by release() would be difficult
: to deallocate reliably, as the source shared_ptr could have been
: created with a custom deleter.

I do not use deleters. And if I do, I would not ask for release. Now I
see that possibly I can simulate "release" with my own deleter (which
will delete or not pointed object, depending on some flag) + get +
reset. This will give me behaviour similar to 2. above. I would really
avoid it, as it makes whole project more complicated (I would need to
manage lifetime of deleters) and error prone.

B.