[boost] [MPL] BOOST_MPL_METAFUNCTION_MAX_ARITY in template_arity

From: Daniel Wallin (dalwan01_at_[hidden])
Date: 2004-08-18 10:08:05

I think there's a mismatch in the use of
BOOST_MPL_METAFUNCTION_MAX_ARITY.

mpl::bind<> and aux::template_arity<> both make use of the
BOOST_MPL_METAFUNCTION_MAX_ARITY when generating code. However, bind<>
has an additional leading argument which increases it's arity by one.
This means template_arity<> will return the wrong arity.

This demonstrates the bug:

   #include <boost/mpl/bind.hpp>
   #include <boost/mpl/lambda.hpp>

   using namespace boost::mpl;

   template<int N, class T>
   void f()
   {
       T x[-1];
   }

   int main()
   {
       f<
           aux::template_arity<bind<int> >::value
         , bind<int>
       >();
   }

With gcc3.3 this results in:

   arity.cpp: In function `void f() [with int N = 5, T =
     boost::mpl::bind<
         int
       , boost::mpl::void_
       , boost::mpl::void_
       , boost::mpl::void_
       , boost::mpl::void_
       , boost::mpl::void_
     >
   ]':

Where N should actually be 6.

-- 
Daniel Wallin