Re: [Boost-users] [signals] Automatic connection management and MT

From: Frank Mori Hess (frank.hess_at_[hidden])
Date: 2007-02-06 20:40:01

On Tuesday 06 February 2007 17:48 pm, Timmo Stange wrote:
> Frank Mori Hess wrote:
> > Okay, here's the partial-template-specialization proof of concept,
> > where polymorphism is confined to a specialization of
> > enable_shared_from_this.
>
> It's a partial template specialization and not all compilers support
> that well enough.   I know that you can work around this and I don't 
> want to be a spoilsport, but I think this is a too intrusive approach
> for the limited purpose it satisfies. What about exception safety
> regarding the call to postconstruct, for example? What if a derived
> class implements postconstruct for its own purposes and doesn't
> forward it up the class hierarchy? Wouldn't you need a predestruct
> for this to be usable for more than your specific needs?

Actually, I've realized there's no reason it has to be tied so closely to 
enable_shared_from_this.  There could be a completely independent base 
class called boost::postconstructible which is treated similarly to 
enable_shared_from_this in shared_ptr.hpp.  Similarly, there could be a 
boost::predestructible base class that gets its hook called before the 
shared_ptr deletes its pointer (perhaps only in the default deleter).  I 
believe the hooks would compile to nothing if the shared_ptr isn't holding 
a pointer derived from one of these classes, just like (I assume) they do 
for enable_shared_from_this.

> I think you're better off writing a specialized smart pointer if you
> want that kind of functionality.

I'm no so keen on a specialized smart pointer, for reasons that you've 
already brought up earlier.  But I suppose that's what I'll do if it comes 
to it.  It shouldn't be too bad to come up with a new name and do a search 
and replace on shared_ptr.hpp.

My point is, enable_shared_from_this was deemed important enough for 
special hooks to be put into shared_ptr.hpp for it.  So there is 
precedent.  And postconstructors/predestructors aren't peculiar ideas that 
I just came up with myself.  I'm sure they could be useful in other 
contexts.

-- 
Frank