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

[Howard Hinnant <hhinnant at apple dot com>]

On Apr 26, 2007, at 7:15 AM, Benjamin Kosnik wrote:

> Also something that struck me as strange is that  
> make_unsigned<wchar_t> gives unsigned wchar_t, but  
> is_unsigned<wchar_t> doesn't work.
>
> Either the algebra seems off, or my understanding is incomplete.

Sorry for the slow response.  I'm not sure what this statement  
means.  Let me start of with my understanding of how these work:

is_unsigned<wchar_t> should return wchar_t(-1) > wchar_t(0).  I'm  
unclear why that doesn't work.

Since there is no such thing as unsigned wchar_t,  
make_unsigned<wchar_t> should give the first out of the following list:

unsigned char
unsigned short
unsigned int
unsigned long
unsigned long long
extended unsigned integer type

which has the same sizeof as wchar_t.

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?

-Howard