[Bug c++/45383] New: [g++ >= 4.5 ] Implicit conversion to pointer does no longer automatically generate operator== and operator!=.

[Bug c++/45383] New: [g++ >= 4.5 ] Implicit conversion to pointer does no longer automatically generate operator== and operator!=.

[seysayux at gmail dot com]

Consider this code:
--------------------
#include <iostream>
struct null {
    null() {}
    template<class T>
    operator T*() const {
        return 0;
    }

    template<class C, class T>
    operator T C::*() const {
        return 0;
    }
private:
    null(const null&);
    null& operator=(const null&);
    void operator&() const;
};

static struct null null;

int main() {
    int* ptr = null;
    std::cout << (ptr == null) << ", " << (ptr != null);
    return 0;
}
--------------------------------
This compiles and gives the expected output ("true, false") on the following
platforms:

http://codepad.org (GCC 4.1, Linux)
Ubuntu 9.10, GCC 4.3
Ubuntu 10.04, GCC 4.4
Mac OS X 10.6, GCC 4.2
Mac OS X 10.6, GCC 4.4
Cygwin, GCC 4.3
Cygwin, GCC 4.4
Unknown Linux variant, Clang 2.8 (trunk 111679) (the "clang" bot on
irc.freenode.net)

However, I get following error on these platforms
-------------
error: no match for 'operator==' in 'ptr == null'
-------------
Cygwin, GCC 4.5
Ubuntu 10.04, GCC 4.5
Unknown Linux variant, GCC 4.6.0 20100507 (the "geordi" bot on
irc.freenode.net)

The people in the irc.freenode.net/##c++ channel confirm that this is indeed
valid C++ code and therefore a bug in GCC.

I do not have ready access to some of these systems (anymore), so I can not say
with certainity what their host, target, or build triplets are.


-- 
           Summary: [g++ >= 4.5 ] Implicit conversion to pointer does no
                    longer automatically generate operator== and operator!=.
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: seysayux at gmail dot com
 GCC build triplet: (many, read below)
  GCC host triplet: (many, read below)
GCC target triplet: (many, read below)


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45383

[Bug c++/45383] [4.5/4.6 Regression] Implicit conversion to pointer does no longer automatically generate operator== and operator!=.

[redi at gcc dot gnu dot org]

------- Comment #1 from redi at gcc dot gnu dot org  2010-08-23 13:17 -------
The summary seems backwards: the conversion shouldn't generate operator==,
instead using operator== should trigger the conversion, but fails to when the
conversion operator is a template.

Strangely, adding a non-template conversion operator causes template argument
deduction to succeed, even though the non-template operator isn't used
e.g.

#include <iostream>
struct null {
    null() {}
    template<class T>
    operator T*() const {
        return 0;
    }

    template<class C, class T>
    operator T C::*() const {
        return 0;
    }
private:
    operator double*() const;  // ???
    null(const null&);
    null& operator=(const null&);
    void operator&() const;
};

static struct null null;

int main() {
    int* ptr = null;
    std::cout << (ptr == null) << ", " << (ptr != null);
    return 0;
}


-- 

redi at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
  GCC build triplet|(many, read below)          |
   GCC host triplet|(many, read below)          |
 GCC target triplet|(many, read below)          |
           Keywords|                            |rejects-valid
   Last reconfirmed|0000-00-00 00:00:00         |2010-08-23 13:17:12
               date|                            |
            Summary|[g++ >= 4.5 ] Implicit      |[4.5/4.6 Regression]
                   |conversion to pointer does  |Implicit conversion to
                   |no longer automatically     |pointer does no longer
                   |generate operator== and     |automatically generate
                   |operator!=.                 |operator== and operator!=.


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45383

[Bug c++/45383] [4.5/4.6 Regression] Implicit conversion to pointer does no longer automatically generate operator== and operator!=.

[hjl dot tools at gmail dot com]

------- Comment #2 from hjl dot tools at gmail dot com  2010-08-23 16:35 -------
It is caused by revision 155415:

http://gcc.gnu.org/ml/gcc-cvs/2009-12/msg00559.html


-- 

hjl dot tools at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dseketel at redhat dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45383

[Bug c++/45383] [4.5/4.6 Regression] Implicit conversion to pointer does no longer automatically generate operator== and operator!=.

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.5.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45383

[Bug c++/45383] [4.5/4.6 Regression] Implicit conversion to pointer does no longer automatically generate operator== and operator!=.

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45383