Re: [Boost-users] [MPL/Fusion?]Call a 0-args template function on members of a sequence

From: Edd Dawson (edd_at_[hidden])
Date: 2006-08-24 15:43:14

David Abrahams wrote:
>>>>   struct call_f
>>>>   {
>>>>      template <class Wrapper>
>>>>      void operator()(Wrapper)
>>> Sorry, it's missing a "const" right here--^^^^
>>>>      {
>>>>          f<typename Wrapper::type>();
>>>>      }
>>>>   };
>>>>
>>>>   mpl::for_each<my_vec, mpl::identity<_> >(call_f());
>> I didn't find this in the docs. Is it meant to be there?
> 
> The specific answer to your specific problem?  No.  Oh yeah, for_each
> wasn't documented in 1.33.1... and apparently it isn't documented in
> the CVS head either (still?  Aleksey?)

Yep, I was referring to mpl::for_each in general.

>> Unfortunately, that didn't quite work for me, anyway. A requirement
>> of for_each (according to my MSVC 8 diagnostics) is that each type
>> in the sequence must be default constructible.
> 
> In the case above, only mpl::identity<T> needs to be
> default-constructible for each type in the list... or that was my
> intention Ach!  My mistake...
> 
>     template <class T> 
>     struct make_identity { typedef mpl::identity<T> type; };
> 
>     mpl::for_each<my_vec, make_identity<_> >(call_f());
> 
> should work.

Like a charm! Many thanks!

Kind Regards,

Edd