[boost] Re: Learning boost::MPL

From: Daniel Wallin (dalwan01_at_[hidden])
Date: 2004-07-01 06:22:22

Dan wrote:

> I'm trying to use iter_fold with a vector_c to compute the sum of all of the
> integers in the container.
> 
> What I have is:
> 
> template<typename Sequence>
> struct sum
> {
> 	typedef typename mpl::iter_fold<
> 		Sequence,
> 		typename mpl::begin<Sequence>::type,
> 		mpl::plus< mpl::deref<_1>, mpl::deref<_2> >; 
> 		// ^ what should this really be?
> 	> // what do i put after here?
> };
> 
> Which obviously won't work. I don't know how to keep a running total as I
> iterate over the sequence with plus.

I don't know why you are using iter_fold instead of just fold here, but
anyway:

   template<typename Sequence>
   struct sum
   {
       typedef typename mpl::iter_fold<
           Sequence
         , mpl::int_<0>
         , mpl::plus<mpl::_1, mpl::deref<mpl::_2> >
       >::type type;
   };

HTH,
-- 
Daniel Wallin