Re: [Boost-users] [boost] [switch_] Compound Cases [was Case Concept]

From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2008-01-14 20:34:01

AMDG

Joel de Guzman wrote:
> Steven Watanabe wrote:
>   
>> My concern is
>> 1) fall-through can't easily be added to the interface.
>>     
>
> I have an idea I'd like to post in another update to the
> case concept.
>   
Great.

> The point is that it is just another case. Whatever the
> sequenced_case is, it's just a model of the case concept.
> Sure it still has to be documented, but not as a separate
> concept, but as a model of it.
>
> Also, to me, it's most trivial to just make it an ET
> tree:
>
>       template< class CaseL, class CaseR >
>       struct binary_case
>       {
>           CaseL l;
>           CaseR r;
>
>           binary_case(CaseL const& l, CaseR const& r)
>              : l(l), r(r) {}
>
>           typedef mpl::joint_view<
>             typename CaseL::labels, typename CaseR::labels
>           > labels;
>
>           template< typename Result, class I >
>           Result apply(I);
>       };
>
> Key points:
>
> * apply is part of the concept. In this case, it dispatches
>    to l or r depending on I
>
> * hmmm.... maybe labels should be an mpl set.
>   

No, thank you.  mpl set is buggy and slow.

Also, one thing that needs to be nailed down is: What Is I?
Tobias was using it as the index into the list of labels:
   mpl::int_<0>, mpl::int_<1>, mpl::int_<2>, ...
In my original interface and as you seem to be using it I is one of:
   mpl::at_c<labels, 0>::type, mpl::at_c<labels, 1>::type, 
mpl::at_c<labels, 2>::type

In Christ,
Steven Watanabe