Re: [Boost-users] [Concept] boost::FloatingPoint<T>

20 Sep 2010

      Dear Dave,

thanks a lot!

Dave Abrahams wrote:
...
On Wed, Sep 15, 2010 at 2:02 PM, Ruediger Berlich
[...]
...
...
From what I understand, this means that I am relying on implementation
details with the above code.
Yes.  Why did you use the undocumente BOOST_concept macro?  That only
exists for backward compatibility with older uses of the BCCL.
This is an almost verbatim copy of the code used for Integer<T>, 
SignedInteger<T> etc. in $BOOSTROOOT/include/boost/concept_check.hpp .
...
...
Is there any way to do the above in a portable way?
// untested
 #include <boost/type_traits/is_floating.hpp>
 #include <boost/mpl/assert.hpp>
template <class T> struct FloatingPoint
 {
     BOOST_MPL_ASSERT((boost::is_floating<T>));
 };
...
P.S.: If the above seems acceptable, please feel free to include it in
Boost.Concept.
If what I suggested works out for you, would you mind submitting a
patch to Trac?
The following example, using your suggestion, works for me (g++ 4.4.3 / 
Ubuntu 10.04). See further below for comments regarding a patch and trac 
item:

//------------------------------------------------------------------------

#include <iostream>
#include <boost/cstdint.hpp>
#include <boost/concept_check.hpp>
#include <boost/type_traits/is_floating_point.hpp>
#include <boost/mpl/assert.hpp>

/*****************************************************************/

namespace boost
{
  template <class T> struct FloatingPoint
  {
    BOOST_MPL_ASSERT((boost::is_floating_point<T>));
  };
}

/*****************************************************************/

template <class T>
class integerWrapper
{
  BOOST_CONCEPT_ASSERT((boost::Integer<T>));

public:
  integerWrapper() { /* nothing */ }
};

template <class T>
class fpWrapper
{
  BOOST_CONCEPT_ASSERT((boost::FloatingPoint<T>));

public:
  fpWrapper() { /* nothing */ }
};

main() {
  integerWrapper<boost::int32_t> iW;
  fpWrapper<double> fW_double;
  fpWrapper<float> fW_float;
  // fpWrapper<char> fW_char; // fails to compile, just as it should
  // fpWrapper<boost::int32_t> fW_int32; // fails to compile, just as it 
should
}

//------------------------------------------------------------------------

It does appear, though, as if the better solution for me would be to 
directly use BOOST_MPL_ASSERT in my code, of which I wasn't aware prior to 
your answer. I've been looking all along for a something that lets me use 
type traits to check the types of an entire template class (instead of just 
single functions, as I've done previously with enable_if).

As to the patch: I'm happy to do this for concept_check.hpp .

Kind Regards / Mit freundlichen Gruessen,
Ruediger Berlich