[Bug c++/46690] New: Using declaration of a dependent name

[Bug c++/46690] New: Using declaration of a dependent name

[ilpoilves at hotmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46690

           Summary: Using declaration of a dependent name
           Product: gcc
           Version: 4.4.5
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ilpoilves@hotmail.com


Consider the following code:

template <typename T>
class A {public: typedef int C;};

template <typename T>
class B: public A<T> 
{
public:
    using typename A<T>::C;
    C operator[](int i) const { return 0; }
};

int main()
{
    B<int> b;
    b[2];
    return 0;
}

The compilation gives:

test.cpp:9: error: ISO C++ forbids declaration of 'C' with no type
test.cpp:9: error: expected ';' before 'operator'
test.cpp:10: error: expected ';' before '}' token
test.cpp: In function 'int main()':
test.cpp:15: error: no match for 'operator[]' in 'b[2]'

A discussion in comp.lang.c++ revealed that this feature was underspecified in
C++03. I propose the using declaration either just to work, or report a proper
error.

To see the intent, consider the current wording for C++0x:

From n3126 (C++0x draft from August 2010), §7.3.3:

"20. If a using-declaration uses the keyword typename and specifies a 
dependent name (14.6.2), the name introduced
by the using-declaration is treated as a typedef-name (7.1.3)."

So the work-around here is 

typedef typename A<T>::C C;

which is equivalent.

The code above is accepted at least by Visual Studio 2008, 2010, and Comeau
C++, all in strict mode.

[Bug c++/46690] Using declaration of a dependent name

[ilpoilves at hotmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46690

--- Comment #1 from ilpoilves at hotmail dot com 2010-11-28 09:38:04 UTC ---
Here is the result of gcc -v, which was left out by accident.

Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.4.4-8'
--with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--enable-multiarch --enable-linker-build-id --with-system-zlib
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc
--with-arch-32=i586 --with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.4.5 20100728 (prerelease) (Debian 4.4.4-8)

[Bug c++/46690] Using declaration of a dependent name

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46690

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2010.11.28 12:08:05
     Ever Confirmed|0                           |1

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2010-11-28 12:08:05 UTC ---
With 4.5 you get a much better error:

use.cc:9:5: error: ‘C’ does not name a type
use.cc:9:5: note: (perhaps ‘typename A<T>::C’ was intended)
use.cc: In function ‘int main()’:
use.cc:15:8: error: no match for ‘operator[]’ in ‘b[2]’

But it should be accepted

[Bug c++/46690] Using declaration of a dependent name

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46690

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |DUPLICATE

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> 2010-11-29 19:13:27 UTC ---
This is the same bug as PR 14258.

*** This bug has been marked as a duplicate of bug 14258 ***