Re: [Boost-users] How shared_from_this() work when it inheritedfrom more than one time

Subject: Re: [Boost-users] How shared_from_this() work when it inheritedfrom more than one time
From: R. P. Janaka (rpjanaka_at_[hidden])
Date: 2009-08-10 05:40:46

Yeah.. exactly this is what I wanted to know..

thank you.

2009/8/10 Björn Karlsson <Bjorn.Karlsson_at_[hidden]>

> Hello R.P,
>
> Inheriting from enable_shared_from_this more than once is not a good idea.
>
> > From: boost-users-bounces_at_[hidden] [mailto:boost-users-
> > bounces_at_[hidden]] On Behalf Of R. P. Janaka
> > Sent: Monday, August 10, 2009 6:54 AM
> > To: boost-users_at_[hidden]
> > Subject: Re: [Boost-users] How shared_from_this() work when it
> > inherited from more than one time
> >
> > But in my case there is no option like this (Class A is a base library
> > class). So I have to do this.
> >
>
> Don't let B inherit from enable_shared_from_this. You've already done that
> in A. So your question then becomes "how do I retrieve a shared_ptr<B> from
> this?". Here's how:
>
>  boost::shared_dynamic_cast<B, A>(shared_from_this());
>
> In the example you've provided, it would also be safe to use
> boost::shared_static_cast.
> To conclude: You should only inherit from enable_shared_from_this in A, and
> B should only inherit from A.
>
> > I did the above to avoid the ambiguous call error So how can I specify
> > that i am calling the shared_from_this() in class B....?
>
> You did. But the problem is that you have two weak_ptrs -- one weak_ptr<A>
> and one weak_ptr<B> -- and only one of them will be initialized correctly
> when you create the smart pointer. (If you're interested in debugging your
> case to really understand what happens, have a look at the function
> sp_enable_shared_from_this() in shared_ptr.hpp.)
>
> Does that help?
>
> Cheers,
> Bjorn Karlsson
>
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>

-- 
Regards,
R. P. Janaka