Re: Branching for 1.1

Olly Betts wrote:
> On Fri, Feb 22, 2008 at 11:57:12AM +0000, Richard Boulton wrote:
>> I'm not sure whether it's safe if the copy constructor or assignment 
>> operator on the subclass are used, though - I'll double-check that.
> 
> I think it will fail, because we expect to be able to do things like:
> 
>     Xapian::Stem copy_of_stemmer = stemmer;
> 
> And that doesn't work if stemmer is a subclass of Xapian::Stem.
> 
> Mind you, making Xapian::Stem wrap an enum doesn't help here either...

I agree.  Argh.

One API for this, then, would be to change Xapian::Stem to be an 
abstract class, and move the implementation to a Xapian::SnowballStem 
class.  However, this would break too much existing code to be a 
reasonable solution, in the near term, anyway.

What about the following:
  - add a Xapian::BaseStem class, which is abstract.
  - make Xapian::Stem inherit from this.
  - change TermGenerator and QueryParser to take a Xapian::BaseStem 
instead of a stem class.

User code would continue to work (after a recompile), but users could 
also create their own subclasses (of BaseStem) and use them with 
TermGenerator and QueryParser.

Really though, what we want is a better reference counting scheme which 
allows the reference counted objects to be subclassed.  Bug 186 is the 
relevant one, I suppose (though coming at it from the opposite direction 
- it's about subclassable objects not being reference counted):
http://xapian.org/cgi-bin/bugzilla/show_bug.cgi?id=186

However, I'm not sure how we could implement this - any ideas?

--

-- 
Richard