Re: c++0x vs. tr1 type_traits, round 1

[Howard Hinnant <hhinnant at apple dot com>]

On Apr 27, 2007, at 7:35 AM, Benjamin Kosnik wrote:

> > If there's anything I can do to help, I'm happy to.  I'd be happy  
> > to post an implementation of make_(un)signed.  It is essentially  
> > built out of type lists (one list for signed integral types and  
> > one list for unsigned integral types).  bool, char and wchar_t,  
> > according to 3.9 are neither, though for sanity purposes, they do  
> > react to is_(un)signed in the intuitive fashion instead of  
> > according to 3.9.  Perhaps this is what you are referring to as  
> > the algebra being off?
>
> I posted a preliminary patch here:
> http://gcc.gnu.org/ml/libstdc++/2007-04/msg00160.html
>
> Your help would certainly be most welcome!

Your patch is so prolific that I've only taken time to review  
make_unsigned.  I will try to be more thorough as time allows.  Thank  
you very much for the effort that you and everyone else is putting  
into this.

I starting building a rough test for make_unsigned and had the  
following failures for your implementation:

Oh, to get started I needed to make a minor tweak on access:

template<typename _Qualified, typename _Unqualified,
   bool _IsConst = is_const<_Qualified>::value,
   bool _IsVol = is_volatile<_Qualified>::value>
  struct __match_cv_qualifiers
  {
//  private:  // hh
    typedef __cv_selector<_Unqualified, _IsConst, _IsVol> __match;
    typedef typename __match::__type __type;
  };

Failed:

__static_assert<is_same<make_unsigned<unsigned char>::type, unsigned  
char>::value> t3;
__static_assert<is_same<make_unsigned<const wchar_t>::type, const  
unsigned>::value> t4;
__static_assert<is_same<make_unsigned<const unsigned>::type, const  
unsigned>::value> t5;

This one failed when compiled with -funsigned-char:

__static_assert<is_same<make_unsigned<char>::type, unsigned  
char>::value> t1;

Fwiw, I've posted a reference implementation (which has a lot of  
similarities to your patch) here:

http://home.twcny.rr.com/hinnant/cpp_extensions/make_signed.html

Hope this helps.  And thanks again for your work on this.

-Howard