Re: [Boost-users] boost-users: boost enable_if

From: chun ping wang (cablepuff_at_[hidden])
Date: 2007-09-26 18:50:50

this question also stems from compiler error generated in microsoft visual
studio 2005 sp1 and microsof visual studio 2008.

It compiles fine under cygwin and mingw.

template <typename T>
bool boost::pseudoprime(const T& n, const T& k)
{
  typedef boost::operators<T> operatorT;
  BOOST_STATIC_ASSERT(is_integral<T>::value || (is_base_of<operatorT,
T>::value)); // mingw says its k, microsoft complains about it.
  BOOST_ASSERT (n > T(2) && n % T(2) != 0);
  return modular_expo(k, n-1, n) != T(1) % n ? true : false;
}

Just trying to get a compiler work around.

On 9/26/07, chun ping wang <cablepuff_at_[hidden]> wrote:
>
> what i want to do is if type "T" happens to be a integeral type *or* a
> class type that inherits from boost::operators than let the function compile
> otherwise a compile time error appears. Basically T is any integeral type or
> any class type that derives from boost::operators.
>
> On 9/26/07, David Abrahams <dave_at_[hidden]> wrote:
> >
> >
> > on Wed Sep 26 2007, "chun ping wang" <cablepuff-AT-gmail.com> wrote:
> >
> > > template <typename T>
> > > bool boost::pseudoprime(const T& n, const T& k)
> > > {
> > >   typedef boost::operators<T> operatorT;
> > >   BOOST_STATIC_ASSERT(is_integral<T>::value); // static assert 1.
> > >   BOOST_STATIC_ASSERT((is_base_of<operatorT, T>::value)); // static
> > assert 2.
> > >   BOOST_ASSERT (n > T(2) && n % T(2) != 0);
> > >   return modular_expo(k, n-1, n) != T(1) % n ? true : false;
> > > }
> > >
> > > now in vistual studio 2005 sp1 and visual studio 2008 beta the part
> > "is_base_of<operatorT,
> > > T>::value" does not work if T happens to be an int or long due to
> > "error C2803: 'operator --'
> > > must have at least one formal parameter of class type". I want to use
> > enable_if to enable the
> > > STATIC_ASSERT only if T is NOT an arithmetic type for static assert 2.
> >
> > enable_if can't "enable static asserts" in any sense that I
> > understand.  What are you really trying to do?  Try to describe it
> > without mentioning enable_if or STATIC_ASSERT.  Just talk about the
> > behavior you want.
> >
> > --
> > Dave Abrahams
> > Boost Consulting
> > http://www.boost-consulting.com
> >
> > The Astoria Seminar ==> http://www.astoriaseminar.com
> >
> > _______________________________________________
> > Boost-users mailing list
> > Boost-users_at_[hidden]
> > http://lists.boost.org/mailman/listinfo.cgi/boost-users
> >
>
>