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

From: Joel de Guzman (joel_at_[hidden])
Date: 2008-01-14 18:58:55

Steven Watanabe wrote:

>>>  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.

Is case_range_c<0, 0> a valid case? If so, it can simply amount
to a no-op (ignored). It won't match anything anyway. But, my
instincts tell me that case_range_c should expect a valid
range.

Regards,
-- 
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net