Re: [boost] [switch_] Case Concept [ was Re: [Boost-users] formal review of Switch library...]

From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2008-01-14 12:01:31

AMDG

Joel de Guzman wrote:
> Steven Watanabe wrote:
>   
>>>      case_<I>(f)             Returns a Case object with supplied
>>> <snip more generators>
>>>   
>>>       
>> These can return fusion sequences of cases instead of plain cases.
>> This has the additional benefit that switch_ can be specified as taking
>> a fusion sequence of cases, without having to handle a single case 
>> specially.
>>     
>
> Right! Makes sense. But wouldn't that use more compile time
> resources? Well, you know better :-)
>   

I don't think so.  I'd have to flatten the sequence anyway.  This way 
you don't pay for
it if you're not using it.

  

>>  From the standpoint of the implementor of switch_, how do I figure out 
>> which
>> Case is the default?
>>     
>
> I thought it would be just a check:
>
>      mpl::empty<C::labels>
>
> But if you want single labels for each Case, then, perhaps:
>
>      is_same<C::label, none>
>
> or somesuch. Am I missing something

Ok.  I didn't like mpl::empty because of the following possibility:

switch_<r>(n)(case_range_c<0, N>(f), default(f));

If N is zero there's a problem.

In Christ,
Steven Watanabe