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

David Abrahams writes:

"Noel Belcourt" writes:

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On Oct 1, 2005, at 6:57 PM, David Abrahams wrote:

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"Noel Belcourt" writes:

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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 >::type>));

One more observation about this, this code doesn't compile if r and p1 are a vector_c or a vector_c 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 r,p1; BOOST_MPL_ASSERT(( equal >::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.

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

Yep. The default predicate for 'equal' is 'is_same', which means that the algorithm compares elements' type identity instead of their values (and for the numeric operations, the former is seldom guaranteed). Try typedef vector_c r,p1; BOOST_MPL_ASSERT(( equal< r , transform >::type , equal_to<_1,_2> > ));

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

I'm actually unsure. Aleksey?

Yes, it is. -- Aleksey Gurtovoy MetaCommunications Engineering