Re: Re: Conversion policies

At 14:09 2003-08-08, David Abrahams wrote:
>Daniel Wallin <[email protected]> writes:
> > OK. Sorry for being vague. I'll try with some short examples:
> >
> > This is the policy system which handles the converter generators and
> > precall/postcall. Consider a typical invoke-function:
> >
> > template<class R, class A0, class A1, class Policies>
> > ret_type invoke(R(*fn)(A0, A1), const Policies& policies)
> > {
> >     // find the converter generators for the given parameter index
> >     typedef typename find_conversion_policy<1, Policies>::type 
> conversion_gen1;
> >     typedef typename find_conversion_policy<2, Policies>::type 
> conversion_gen2;
> >
> >     // generate a converter for the associated type
> >     typename conversion_gen1::template generate_converter<A0,
> >     xxx_to_cpp>::type c1;
> >     typename conversion_gen2::template generate_converter<A1,
> >     xxx_to_cpp>::type c2;
> >
> >     // the converter objects are later applied to the parameter passed 
> from the
> >     // interpreter state to get the actual parameters.
> > }
>
>OK, I understand now.
>
>here's what I was thinking might make for a more efficient
>implementation.  Instead of using all of that TMP inside of every
>wrapped function implementation, arrange the policies type so that it
>can do all the work with overloading:
>
>template<class R, class A0, class A1, class Policies>
>ret_type invoke(R(*fn)(A0, A1), const Policies& policies, ArgTuple t)
>{
>     if !(
>          policies.check(_1, identity<A0>(), t[0])
>        , policies.check(_2, identity<A1>(), t[1])
>     )
>     return kOverloadFailed;
>
>     return policies.from_cxx(
>         fn(
>              policies.to_cxx(_1, identity<A0>(), t[0])
>            , policies.to_cxx(_2, identity<A1>(), t[1])
>         )
>     );
>}
>
>Just a thought.

That's pretty nice, but wouldn't the forwarding cause problems with the return
type? What should to_xxx() return?

---
Daniel Wallin



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