[Boost-users] [Ref] unwrap_ref and TR1

Subject: [Boost-users] [Ref] unwrap_ref and TR1
From: Krzysztof Żelechowski (giecrilj_at_[hidden])
Date: 2011-12-14 15:11:03

The following code is valid:

#if 1
#include <boost/ref.hpp>
int const & (&b_unwrap_ref) (int const &) ((::boost ::unwrap_ref));
#endif

The following code, however, is not (as of libstdc++ 4.5.1):

#if 1
#include <tr1/functional>
int const & (&tr1_unwrap_ref) (int const &) ((::std ::tr1 ::unwrap_ref));
#endif

With the following diagnostic:

 > error: ‘unwrap_ref’ is not a member of ‘std::tr1’

So I started to ask myself: WTF?
* It turns out that unwrap_ref did not make it to TR1, although 
reference_wrapper did.

But why?
* Because ref.hpp did not provide it when TR1 was formed? [1]

Implication:
* unwrap_ref (std:: reference wrapper) is a mismatch.

#if 1
void test () {
  unwrap_ref (::boost ::cref (0));
  unwrap_ref (::std ::tr1 ::cref (0)); // error: ‘unwrap_ref’ was not 
declared in this scope
  ::boost ::unwrap_ref (::std ::tr1 ::cref (0)); // error: error: 
invalid initialization of non-const reference
}
#endif

Shouldn't we do something about it?  Like, e.g., extend the scope of 
unwrap_ref to cover the corresponding standard class?
This would at least allow expression #3.

Chris

___
[1] <URL: 
https://svn.boost.org/svn/boost/!svn/bc/16384/trunk/boost/boost/ref.hpp >