Re: [Boost-users] shared_ptr invalid covariant return type

From: Frank Mori Hess (frank.hess_at_[hidden])
Date: 2008-06-24 12:01:28

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On Tuesday 24 June 2008 11:13 am, John wrote:
> Thanks, I did see that in the archives before I posted. Please correct me
> if I'm wrong, but the code from 2003 doesn't provide a solution, since the
> clone() method is not virtual. i.e.,  you can't do this with it:
>
>    shared_ptr<A> a = foo();
>    shared_ptr<A> a2 = a->clone ();
>
> which is the goal of the pattern.

The free function solution mentioned in the post calls the virtual do_clone.  
The virtual do_clone always returns a shared_ptr to the base class, and the 
template free function downcasts it.  The free function has to be a friend, 
(or do_clone public).
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