[Boost-users] Assertions doesn't work!

From: Kiuhnm (kiuhnm03_at_[hidden])
Date: 2006-04-05 14:18:23

I'm using MSVC8 (2005) with Boost 1.33.1.
The code at the end of this post should cause the compiler to print out
something like this (GCC):

conversion from 'mpl_::failed
    ****************(factorial<mpl_::int_<-5>
    >::FACTORIAL_of_NEGATIVE_NUMBER::****************)
    (mpl_::int_<-5>)' to non-scalar type 'mpl_::assert<false>'
    requested.

but I obtain something completely different.
It seems that the compiler continues to evaluate the factorial (-1, -2, -3,
...) ignoring the assertions. Since the template expansion is quite
"complex", the compiler fails and prints out:

---
fatal error C1202: recursive type or function dependency context too complex
       
c:\boost\include\boost-1_33_1\boost\mpl\aux_\preprocessed\plain\times.hpp(60)
: see reference to class template instantiation 'factorial<N>' being
compiled
        with
        [
            N=boost::mpl::int_<-88>
        ]
---
What's wrong?
---
#include <boost/mpl/assert.hpp>
#include <boost/mpl/greater_equal.hpp>
#include <boost/mpl/equal_to.hpp>
#include <boost/mpl/multiplies.hpp>
#include <boost/mpl/prior.hpp>
#include <boost/static_assert.hpp>
namespace mpl = boost::mpl;
// specializations are nullary metafunctions that compute n>0
template <int n>
struct FACTORIAL_of_NEGATIVE_NUMBER
 : mpl::greater_equal<mpl::int_<n>, mpl::int_<0> >
{};
template <class N>
struct factorial
 : mpl::eval_if<
       mpl::equal_to<N,mpl::int_<0> >
     , mpl::int_<1>
     , mpl::multiplies<
           N
         , factorial<typename mpl::prior<N>::type>
       >
   >
{
   BOOST_MPL_ASSERT((FACTORIAL_of_NEGATIVE_NUMBER<N::value>));
   BOOST_STATIC_ASSERT((0));     // !!!
   BOOST_MPL_ASSERT_MSG(N::value >= 0, FACTORIAL_of_NEGATIVE_NUMBER, (N));   
// !!!
};
int main()
{
	int f = factorial< mpl::int_<-5> >::type::value;
}
---
Thank you, Kiuhnm
--
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