Re: Re: Registries [2]

At 13:47 2003-07-29, David Abrahams wrote:
>Daniel Wallin <[email protected]> writes:
>
> > At 13:51 2003-07-28, David Abrahams wrote:
> >>Yes, I meant essentially that all local chains for a type would share
> >>a tail: the corresponding global chain.
> >
> > Ok, I've been thinking about this.
> >
> > The biggest problem I can see with this is that we can't eliminate
> > duplicate converters, if a module registers a converter for type X
> > it will get a duplicate in the global chain. Of course things will
> > still work as expected, but overload resolution will suffer in terms
> > of performance since we'd need to try more converters before we can
> > conclude that there's no match.
>
>Oh, I guess.  I don't really think failed matches have to be fast, but
>I also don't really care if you want to use a more-sophisticated
>mechanism to optimize them.

It's not the failed matches, but the entire overload resolution that needs
to be fast. If there were no overloads, we wouldn't have a problem.

> > Also, identical converters registered by multiple modules can't be 
> separated,
> > so we'd end up with a lot of identical converters for primitive types.
> > I guess we could keep all primitive converters in the shared
> > library.
>
>I don't see "where they are kept" quite the same way you do, I
>think -- it's all one shared memory space.  However, yeah, the shared
>lib should register those primitives itself.  That's what
>Boost.Python does now.

Yeah, I meant that the primitives could reside only in the global chain..

> > This is an issue with automatic importing in general though.
>
>Not sure I see an issue.

I meant the issue with unnecessary long converter chains, mostly due to
duplication.

I'm starting to doubt our motives for local registries altogether, I might
be forgetting something or I might be drunk, but right now it seems to me
that we'd be better off with only a global registry. I just can't think of 
any cases
where there would be interest in hiding converters. This is quite a 
turnover for
me, so if someone could convince me that there are benefits with local 
registries
I'd be glad. ;)

---
Daniel Wallin



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