Re: [sigc] derive from sigc::trackable directly?

["John K. Grant" <grant cyrf com>]

Hi,
This is might be my first post, I've enjoyed reading this list for a 
while, but I'm a newbie, so bare with me.

Does a class actually *need* to derive from trackable?  Can one 
implement an auto-disconnect feature in one's Base class without using 
trackable?  I am working with an engine whose base class supports 
signals/slots, but is also reference counted.  The authors chose to use 
multiple inheritance, deriving from trackable and a Referenced class.  I 
would like to help eliminate this multiple inheritance, so I was 
wondering if it is necessary to derive from trackable.

Also, has this thread ended?  What was the resulting recommended usage?
Thank you much, -John


Dick Eimers wrote:
> > When DerivedX derives from sigc::trackable as you show, the order is
> > the same (IIRC), but in this case it depends on the order, i.e.
> >    struct X: base, sigc::trackable{..};
> > is not equivalent to
> >    struct X: sigc::trackable, base{..};
> >     
>
> You remember correctly and I should have paid more attention to this..
>
>   
> > Auto-disconnecting is fundamentally flawed when achieved via this
> > baseclass. The problem is that if you derive from a class, there is a
> > time between ~derived() is called and when it is disconnected in
> > ~trackable(). If in between a call to one of its slots is done, these
> > slots end in nirvana. I'd say the solution is to disconnect in the
> > most derived dtor manually.
> >     
>
> This explanation sounds plausible except for the "[..] the solution is
> to disconnect in the most derived dtor manually"-part. It heads for
> auto-disconnecting being fundamentally flawed. 
>
> Is manually disconnecting considered to be the best practice and should
> sigc::trackable be avoided and used only with flat-hierarchies?
>
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