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

From: David Abrahams (dave_at_[hidden])
Date: 2005-10-02 20:35:01

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

> On Oct 1, 2005, at 6:57 PM, David Abrahams wrote:
>
>> "Noel Belcourt" <kbelco_at_[hidden]> writes:
>>> 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_MPL_ASSERT((equal<r, transform<r, p1, or_<_,_> >::type>));
>
> One more observation about this, this code doesn't compile if r and p1 
> are a vector_c<bool,..> or a vector_c<int,..> with CW 9.5 on Tiger 
> 10.4.2.  The compiler output is attached.
>
> For example, if r and p1 are declared as follows, the code will not 
> compile.
>
> typedef vector_c<bool,1,0> r,p1;
> BOOST_MPL_ASSERT(( equal<r, transform<r, p1, or_<_,_> >::type>));
>
> The problem seems to be that the sequence produced by invoking 
> transform using a boolean binary function is a different type than 
> vector_c<bool,..>.  

I think that's not really the issue.  I think the problem is that the
_element_ types of those two sequuences are not identical.

> The fix is trivial.
>
> typedef vector_c<bool,1,0> r,p1;
> BOOST_MPL_ASSERT(( equal<transform<r, r, and_<_,_> >::type, 
> transform<r, p1, or_<_,_> >::type>));
>
> While clunky, this works, and also works if we declare r and p1 as 
> vector_c<int,..>.

Actually I think that's technically nonportable.

I'm guessing the right thing to do is use find, one way or the other.
This is 

  typedef transform<r, p1, not_equal_to<_1, or_<_,_> > >::type x;
  BOOST_MPL_ASSERT(( 
      is_same<
          find_if<x,_1>::type
        , end_<x>::type
       >
   ));

> Just want to be sure that this is known and expected behavior?

I'm actually unsure.  Aleksey?

>>   BOOST_MPL_ASSERT((
>>       equal_to<

I think this should be is_same.  Sorry for the mistake.

>>           find<
>>               zip_view<r,p1>
>>             , not_equal_to<first<_>,or_<first<_>,second<_> >
>>> ::type
>>         , end<zip_view<r,p1> >::type
>>>
>>   ))
>
> I'll be sure to read up on zip_view and try this out.
>
> Thanks for your help.
>
> -- Noel
>
>
>
>
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-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com