[Boost-users] [thread_safe_signals] postconstructors and predestructors

From: Frank Mori Hess (fmhess_at_[hidden])
Date: 2007-02-06 21:57:57

> 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. 
> 

Now I realize I don't need any changes to shared_ptr at all, I can do it 
all in a wrapper function inserted between the raw pointer and shared_ptr.  
I can't think of a name, so call it ptr_wrapper():

shared_ptr<MyClass>(signalslib::ptr_wrapper(new MyClass));

ptr_wrapper would call postconstruct() if its input pointer is derived from 
postconstructible, and return a shared_ptr.  The deleter for the returned 
shared pointer would be (by default) customized to call the predestructor 
if the input pointer is derived from predestructible.  A custom deleter 
could be accepted as a second argument to ptr_wrapper.

--  
Frank