libstdc++/5133: Problems with toupper

[Christopher Currie]

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&p
r=5133

Sorry to dig up this old PR, but it seems to still be in feedback state, and
I've been working with the problem recently and I wanted to weigh in.

Philip Martin wrote:
> using the function template is
> tricky because the second parameter is a reference. One would like to
> try
>
>   // this won't work
>   std::locale loc;
>   std::transform(s.begin(),s.end().s.begin(),
>                  std::bind2nd(std::ptr_fun(std::tolower<char>),loc));
>
> but this will suffer from the reference to a reference problem.

Without going into too much detail, the problem is detected in binder2nd's
constructor, but can be traced to the definition of the binary_function
template. I was able to get the above code working by adding a
specialization of the template, used when the second argument is a
reference:

#include <functional>
#include <algorithm>
#include <string>
#include <locale>

namespace std
{
// specialization for the second argument being a reference
template <class _Arg1, class _Arg2, class _Result>
struct binary_function<_Arg1, _Arg2&, _Result> {
  typedef _Arg1 first_argument_type;
  typedef _Arg2 second_argument_type;
  typedef _Result result_type;
};
}

int main()
{
  using namespace std;
  string s ("Someone Chanted Evening");
  locale loc;

  transform(s.begin(), s.end(), s.begin(),
      bind2nd(ptr_fun(&tolower<char>), loc));

  return 0;
}

Naturally, a second specialization would be necessary for the first
argument, so that bind1st will also behave as expected.

The remaining questions: Does this specialization violate the Standard,
and/or will it break existing code?

Comments and criticisms welcome.

Christopher Currie