Re: [boost] [smart_ptr] Some questions

From: Frank Mori Hess (frank.hess_at_[hidden])
Date: 2008-04-09 14:16:10

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On Wednesday 09 April 2008 14:07 pm, Daniel Frey wrote:
> On Wed, 2008-04-09 at 13:47 -0400, Frank Mori Hess wrote:
> > On Wednesday 09 April 2008 11:13 am, Daniel Frey wrote:
> > > I have use cases which would be a lot easier to implement if
> > > shared_from_this() never throws. And - at least with the "old"
> > > implementation - I don't see any reason why this guarantee should not
> > > hold. Of course it's not a defect, but to me it seems desirable.
> >
> > It is technically possible to make it throw without violating the
> > functions documented requirements, if there are multiple owners.  For
> > example, if pass the raw pointer to multiple shared_ptrs with null
> > deleters.
>
> Could you provide a small but complete code example, please? I fail to
> see how that case should be legal.

Here you go, this throws against the old library.  It doesn't against the 
trunk, due to a slight change in behavior, but could easily be modified to do 
so.

- -- 
Frank
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#include <boost/enable_shared_from_this.hpp>
#include <boost/shared_ptr.hpp>

void null_deleter(const void*)
{}

class myclass: public boost::enable_shared_from_this<myclass>
{};

int main()
{
        myclass *myobj = new myclass;
        boost::shared_ptr<myclass> ptr(myobj);
        {
                boost::shared_ptr<myclass> ptr2(myobj, &null_deleter);
        }
        ptr->shared_from_this();
        return 0;
}

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