Re: [boost] Re: result_ofOp, operator should be a template parameter

From: Doug Gregor (dgregor_at_[hidden])
Date: 2004-07-03 18:58:04

On Jul 3, 2004, at 6:47 PM, Andy Little wrote:
> I have seen this, but BTW I cant find the
> utilities/detail/result_of_iterate.hpp header in the boost CVS

??? It's there (and the regression tests are finding it). Are you using 
"cvs update -d"?

> result_of is a a general purpose tool. My point is that when dealing 
> with
> 'operators' as opposed to functions in general it is  much more 
> convenient
> to have one one class representing the operation than a plethora of
> result_of_xxx  classes. Take a look in Lambda, Ublas etc etc... 
> currently
> they all do their own thing on operators

If we had "smarter" versions of std::plus, std::minus, etc. that played 
well with result_of, I think that would solve the issue reasonably 
well.

> One common interface class (ie binary_operation) for operators would 
> sure
> help when designing matrix operators etc. To do that you need a 
> template
> parameter capable of representing the generic operation.

... which is just a function object. Something like this:

struct minus
{
   template<typename> struct result;

   template<typename F, typename T, typename U>
     struct result<F(T, U)>
     {
       typedef *magic* type;
     };

   template<typename T, typename U>
     typename result<minus(T, U)>::type operator()(T t, U u)
    { return t+u; }
}

        Doug