Specializations of std::char_traits

[Matt Austern <austern at apple dot com>]

We've received several complaints from customers who noticed that 
std::char_traits<int> (or long, or signed char, or unsigned short, or 
whatever) used to be defined but isn't defined anymore.

Now, just to be obvious, I realize that
 - The C++ standard doesn't say there should be any specializations 
other than char and wchar_t
 - In general there's no way to define all of the members of 
std::char_traits for an arbitrary type.  There's no good way to say 
what char_traits<T>::int_type should be, for example.

But still, think about it from the user perspective: with 3.1 users 
were able to write std::basic_string<int>, and now, when they try, 
they'll get mysterious link-type errors dealing with some machinery 
they've never heard of and don't care about.  Even if the standard 
doesn't guarantee the ability to have a basic_string<int>, users are 
bound to see this change as a regression.  And, unfortunately, it's not 
a regression with a very good workaround.  (Users can't specialize 
std::char_traits for fundamental types.)

What would people think of reintroducing a stub generic char_traits, 
one that defines just enough functionality for std::basic_string to 
work?  That's what other compilers do. If we don't do it, I think we'll 
get more complaints.

(And I'll also pester the LWG issues list maintainer to open a library 
issue on this for C++0x.)

			--Matt