Re: Conversion policies

Daniel Wallin <[email protected]> writes:

> At 16:00 2003-08-08, David Abrahams wrote:
>>Daniel Wallin <[email protected]> writes:
>>
>> > Ok I've given this some thought. The issue is that we need to keep the
>> > converter
>> > object instances on the stack of the invoker function, to be able to have
>> > storage between check() and to_cxx(). This is important for
>> lvalue-conversions
>> > which can perform the entire conversion in the checking part, and
>> stores the
>> > pointer. It's likely important for other more advanced policies as
>> well, which
>> > could need intermediate storage.
>>
>>Right, OK:
>>
>>template<class R, class A0, class A1, class Policies>
>>ret_type invoke(R(*fn)(A0, A1), const Policies& policies, ArgTuple t)
>>{
>>     typename Policies::conversions_type converters(policies);
>>
>>     if !(
>>          converters.check(_1, identity<A0>(), t[0])
>>        , converters.check(_2, identity<A1>(), t[1])
>>     )
>>     return kOverloadFailed;
>>
>>     return converters.from_cxx(
>>         fn(
>>              converters.to_cxx(_1, identity<A0>(), t[0])
>>            , converters.to_cxx(_2, identity<A1>(), t[1])
>>         )
>>     );
>>}
>
> The type of the converter objects is dependent on the types they
> operate on, so
> it's slightly more complicated:
>
> typename Policies::template conversions_type<
>       mpl::list<A0, A1>
>    >::type converters;
>
> Which isn't really more efficient than the first implementation. Less
> code in the invoker
> functions though.


Ah, right.  Anyway, it's too early to be optimizing compilation speed
here.

I'm convinced ;->

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com



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