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

At 22:51 2003-09-24, David Abrahams wrote:
>Daniel Wallin <[email protected]> writes:
>
> > At 12:35 2003-09-23, David Abrahams wrote:
> >>Daniel Wallin <[email protected]> writes:
> >>
> >> > 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.
> >>
> >>Name hiding could cause a problem there... unless... we could have a
> >>using declaration built into the components to get around that.
> >
> > Right.
> >
> >     template<class Base, class T>
> >     struct tuple_elem
> >        : Base, T
> >     {
> >        using Base::f;
> >        using T::f;
> >     };
> >
> >     struct empty_type
> >     {
> >        void f();
> >     };
> >
> >     typedef inherit_linearly<
> >           sequence_t
> >         , tuple_elem<_,_>
> >         , empty_type>::type composite_t;
> >
> > Would work I guess. But that puts some additional requirement on the
> > convert() signature..
>
>You mean just matching the argument index?  Big deal(?)

No, not a big deal. But we should care about every additional requirement
on the interface.. This does seem like a nice way to do things though.

---
Daniel Wallin




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