Re: [boost] [MPL] Integral constant expressions and MSVC.

From: Aleksey Gurtovoy (agurtovoy_at_[hidden])
Date: 2004-05-21 12:32:32

Cromwell Enage writes:
> Morning, all.

Hi Cromwell,

> I'm trying to implement a compile-time greatest common
> divisor metafunction, 

This one already exists in Boost, although its location is
somewhat unexpected; please take a look at math/common_factor 
library, http://www.boost.org/libs/math/doc/common_factor.html.

> a key component of which is
> boost::mpl::modulus_c.  Am I correct if I say that the
> following is typical usage of this class template?
> 
> #include <iostream>
> #include <boost/mpl/modulus.hpp>
> 
> int main()
> {
>     typedef typename
              ^^^^^^^^

'typename' is not allowed outside of templates.

> boost::mpl::modulus<int,14,6>::type
              ^^^^^^^

I suppose you meant 'modulus_c', here.

>             remainder_type;
> 
>     std::cout << "The remainder of 14 divided by 6 is";
>     std::cout << remainder_type::value << std::endl;
> 
>     return 0;
> }
> 
> MinGW 3.2 accepts this usage, but MSVC 7.1 files the
> following complaint:
> 
> ..\..\Libraries\boost\boost\mpl\modulus.hpp(39) :
> error C2975: 'N' : invalid template argument for
> 'boost::mpl::integral_c', compile-time evaluatable
> constant expression expected
> 
> It seems MSVC doesn't recognize A % B as an integral
> constant expression.

Hmm, if I make the above fixes, it compiles fine for me. May be
the problem disappeared when you reduced the code for the post?

> 
> What's the proper way of handling this?

Fixing the library, which I'll happily do if we can reproduce 
the issue.

--
Aleksey Gurtovoy
MetaCommunications Engineering