[Bug c++/50471] New: Qualified lookup fails to find template function

[Bug c++/50471] New: Qualified lookup fails to find template function

[zoltan at epochcapital dot com.au]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50471

             Bug #: 50471
           Summary: Qualified lookup fails to find template function
    Classification: Unclassified
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: zoltan@epochcapital.com.au


Please see the attached sample file, functions g1() and g2() should produce the
same output, but they do not. The difference is that g2() finds a template
function when called with an unqualified name, g1() does not find the template
function when called with a qualified name. 

GCC version:

[zoltan@epcau-srv-dev:test]$ g++-4.5 -v
Using built-in specs.
Reading specs from /usr/lib64/gcc/x86_64-suse-linux/4.5/defaults.spec
COLLECT_GCC=g++-4.5
COLLECT_LTO_WRAPPER=/usr/lib64/gcc/x86_64-suse-linux/4.5/lto-wrapper
Target: x86_64-suse-linux
Configured with: ../configure --prefix=/usr --infodir=/usr/share/info
--mandir=/usr/share/man --libdir=/usr/lib64 --libexecdir=/usr/lib64
--enable-languages=c,c++,fortran --enable-checking=release
--with-gxx-include-dir=/usr/include/c++/4.5 --enable-ssp --disable-libssp
--disable-plugin --with-bugurl=http://bugs.opensuse.org/
--with-pkgversion='SUSE Linux' --disable-libgcj --disable-libmudflap
--with-slibdir=/lib64 --with-system-zlib --enable-__cxa_atexit
--enable-libstdcxx-allocator=new --disable-libstdcxx-pch
--enable-version-specific-runtime-libs --program-suffix=-4.5
--enable-linux-futex --without-system-libunwind --enable-gold
--with-plugin-ld=/usr/bin/gold --with-arch-32=i586 --with-tune=generic
--build=x86_64-suse-linux
Thread model: posix
gcc version 4.5.0 20100414 [gcc-4_5-branch revision 158342] (SUSE Linux)

[Bug c++/50471] Qualified lookup fails to find template function

[zoltan at epochcapital dot com.au]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50471

--- Comment #1 from Zoltan Glozik <zoltan at epochcapital dot com.au> 2011-09-21 05:41:57 UTC ---
Created attachment 25330
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25330
bug

[Bug c++/50471] Qualified lookup fails to find template function

[zoltan at epochcapital dot com.au]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50471

--- Comment #2 from Zoltan Glozik <zoltan at epochcapital dot com.au> 2011-09-21 05:43:44 UTC ---
Comment on attachment 25330
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25330
bug


#include <iostream>

namespace NS {

template<class T>
struct A {
    T t;
};


template<class T>
void f(T &t)
{
    std::cout << "function 1" << std::endl;
}       

template<class T>
void g1(T &t)
{
    // qualify with namespace
    NS::f(t);
}

template<class T>
void g2(T &t)
{
    // do not qualify with namespace
    f(t);
}

template<class T>
void f(A<T> &t)
{
    std::cout << "function 2" << std::endl;
}

}

int main()
{
    using namespace NS;
    A<int> a;

    g1(a);      // this should print: "function 2", bug?
    g2(a);      // this prints "function 2" correctly.
    return 0;
}

[Bug c++/50471] Qualified lookup fails to find template function

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50471

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-09-21 06:18:32 UTC ---
    NS::f(t);
Binds at the point at definition because it is qualified.
    f(t);
Does not bind and then does argument dependent lookup (ADL) at instantiation
time.

[Bug c++/50471] Qualified lookup fails to find template function

[zoltan at epochcapital dot com.au]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50471

--- Comment #4 from Zoltan Glozik <zoltan at epochcapital dot com.au> 2011-09-21 06:43:29 UTC ---
(In reply to comment #3)
>     NS::f(t);
> Binds at the point at definition because it is qualified.
>     f(t);
> Does not bind and then does argument dependent lookup (ADL) at instantiation
> time.

Thanks. According to the C++ spec I have the lookup of names dependent on the
template parameters is postponed until the actual template argument is known,
and in this case NS::f() is dependent on a template argument, so I would think
the lookup would be delayed till instantiation. Can you please point me to the
paragraph in the standard that says qualified names bind at definition even if
they depend on a template argument.

[Bug c++/50471] Qualified lookup fails to find template function

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50471

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-09-21 10:19:21 UTC ---
The name lookup is delayed until instantiation, however [temp.dep.candidate]
says that the qualified lookup in g1 only finds declarations visible at the
point of definition of g1:

For a function call that depends on a template parameter, the candidate
functions are found using the usual lookup rules (3.4.1, 3.4.2, 3.4.3) except
that:
— For the part of the lookup using unqualified name lookup (3.4.1) or qualified
name lookup (3.4.3), only function declarations from the template definition
context are found.
— For the part of the lookup using associated namespaces (3.4.2), only function
declarations found in either the template definition context or the template
instantiation context are found.

[Bug c++/50471] Qualified lookup fails to find template function

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50471

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-09-21 10:22:48 UTC ---
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#448