Re: [Boost-users] [Boost][mpl] vector_c boolean operations

From: David Abrahams (dave_at_[hidden])
Date: 2005-10-01 19:57:28

"Noel Belcourt" <kbelco_at_[hidden]> writes:

> Let me see if I understand this.
>
> So if I want to perform an element-wise mpl::or operation of two 
> sequences (r, p1) and then test the resulting sequence for equivalence 
> to the input sequence, something like this should work since as you 
> observe below, mpl::equal will compare two sequences and yield a scalar 
> boolean.
>
> BOOST_STATIC_ASSERT((
>    equal<
> 	r
>         , transform<r,p1,or_<_,_> >::type
>    >::type::value
> ));

Yes.

  BOOST_MPL_ASSERT((equal<r, transform<r, p1, or_<_,_> >::type>));

would be nicer and give better messages.  And other things might be
much more efficient, e.g.

  
  BOOST_MPL_ASSERT((
      equal_to<
          find<
              zip_view<r,p1>
            , not_equal_to<first<_>,or_<first<_>,second<_> >
          >::type
        , end<zip_view<r,p1> >::type
      >
  ))

>> Second, you seem to be trying to use the equal algorithm, which
>> operates on sequences, on the results of some invocation of mpl::or_,
>> which does not return a sequence but a scalar bool-valued MPL integral
>> constant.
>
> True, I was confused about this point.  So I'll use transform to 
> generate a sequence representing the element-wise binary operation and 
> then use equal.

Great; good luck!

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com