Re: Re: [C++-sig] [Implementation] Calling wrapped functions, converters, policies

At 14:46 2003-09-22, David Abrahams wrote:
>Daniel Wallin <[email protected]> writes:
>
> > At 18:53 2003-09-21, David Abrahams wrote:
> >>Daniel Wallin <[email protected]> writes:
> >>
> >> >>Actually I was thinking that the index should be encoded in the type
> >> >>of the converter.
> >> >
> >> > Ok, both approaches work.
> >>
> >>I think we may have single converter tuple at this point.  If so we'll
> >>want something like:
> >>
> >>        converters.convert(argument_package,mpl::int_<1>());
> >
> > I have expressed some concern on this before due to the issue with an
> > additional layer when returning temporaries from convert().
> > (with const& argument types..)
> >
> > I would rather see something like:
> >
> >     get<0>(converters).convert(argument_package);
> >
> > or
> >
> >     get<0>(converters).convert(argument_package, mpl::int_<0>());
>
>I'm sorry, I don't see why one should be more problematic than the
>other, but I'm willing to go with your first alternative if you like.
>I think the 2nd one is unneccessary.

It's problematic because of how the 'converters tuple' type would be
implemented. I guess it could be implemented with inheritance,
and require that converters take an mpl::int_<N> where N is their
index. But as I saw this it would probably be implemented with
a forwarding function, which would obviously cause problems if
the converter would return a temporary which should bind to a
const&.

Now that I think about it it wouldn't be that problematic to implement
with inheritance instead, although it does complicate the convert()
signature a bit.

---
Daniel Wallin




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