[boost] Re: Patterns (was Singleton)

From: Dave Handley (dave_at_[hidden])
Date: 2005-01-13 03:00:30

Jeff Garland wrote:

>
> Well, my feedback is going to be fairly shallow since I don't have lots of
> time to look it over, but what I see looks pretty good.  Both of the 
> composite
> and visitor stuff would be nice additions.
>

Thanks :-)

> One interesting question on composite is whether a boost::tree would 
> really be
> all that's needed and might be a more general component that could be used 
> to
> implement composite.  Of course, you are really depending on pointer 
> semantics
> and the clone, so it wouldn't be a minor change of course to go down that 
> path...
>

I'm pretty sure that the implementation I have of the composite would also 
work as a tree if you didn't use CRTP.  I've not tested this, but just 
browsing my own code convinces me of it!  I personally think that 
improvements could be made to the composite by incorporating some policies. 
I've not given this much thought, but options could include a memory 
management policy that allowed you to choose between: the current model with 
pointers and clone; a single type in the tree that used copy and value 
semantics; a smart_ptr based model.

> I think instead of trying to create a 'patterns' library I would make 2
> standalone libraries: vistor and composite.  The fact that these are
> 'patterns' (ie: well known designs) isn't really strong enough to bind 
> them
> together.
>

My reason for wanting to create a patterns library is actually from a desire 
to try and create a Loki equivalent in boost (with some additions).  The 
inter-play between certain patterns is such that I think they could sit in 
the same library.  For example, the work I've done on visiting composite 
trees, or the fact that an abstract factory is often a singleton, etc. 
Having said that, I would not be averse to them being different libraries if 
that was preferred.

Dave