[v3] ext/type_traits.h

[Martin Sebor]

Howard Hinnant wrote:
> On Sep 28, 2006, at 4:45 PM, Martin Sebor wrote:
> 
>> Peter Dimov wrote:
>>
>>> Martin Sebor wrote:
>>>
>>>> The standalone add_unsigned critters would be okay too. They
>>>> would be in line with all the other little traits classes. I
>>>> don't see a big advantage of one approach over the other.
>>>
>>> The standalone to_unsigned can be used as a metafunction.
>>
>>
>> Ah, neat. I hadn't thought of that. And the limits one couldn't
>> because...? It doesn't have the right name?
> 
> 
> Iiuc, yes.  Here's a trivial trait that takes a metafunction as a  
> template template parameter (F):

Cool. Thanks for the demo!

[...]
> One might imagine some similar test or trait where supplying  
> add_unsigned would work, because it has a nested "type", and  
> numeric_limits would fail.

Hmm, looks like we need a "metafunction adapter" for legacy
interfaces:

   template <class T>
   struct make_type { typedef T type; };

That way make_type<numeric_limits<T>::unsigned_type>::type could
be used as a metafunction too ;-)

Martin