[Bug c++/34023] New: Wrong using of user-defined conversion operator for converting rvalue to reference on constant.

[Bug c++/34023] New: Wrong using of user-defined conversion operator for converting rvalue to reference on constant.

[sergey dot gcc at comrades dot id dot au]

// gcc version 3.4.5 (mingw-special)
class a
{
public:

        template<class T>
        operator T &() const
        {
                static int f;
                return f; // line # 10
        }

        /* 
        // unsafe workaround:
        operator a const &() const
        {
                return *this;
        }
        */
};

int main()
{
        // : In member function `a::operator T&() const [with T = const a]':
        // :27:   instantiated from here
        // :10: error: invalid initialization of reference of type 'const a&'
from expression of type 'int'
        a const &aa = a(); // line # 27
        /*
        // workaround:
        a const temp;
        a const &aa = temp;
        */
}


-- 
           Summary: Wrong using of user-defined conversion operator for
                    converting rvalue to reference on constant.
           Product: gcc
           Version: 3.4.5
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: sergey dot gcc at comrades dot id dot au


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34023

[Bug c++/34023] Wrong using of user-defined conversion operator for converting rvalue to reference on constant.

[sergey dot gcc at comrades dot id dot au]

------- Comment #1 from sergey dot gcc at comrades dot id dot au  2007-11-08 01:58 -------
I've checked other versions of compiler, such as 3.4.6 and 4.X.X. Can someone
check?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34023

[Bug c++/34023] Wrong using of user-defined conversion operator for converting rvalue to reference on constant.

[sergey dot gcc at comrades dot id dot au]

------- Comment #2 from sergey dot gcc at comrades dot id dot au  2007-11-08 02:03 -------
(In reply to comment #1)
> I've checked other versions of compiler, such as 3.4.6 and 4.X.X. Can someone
> check?
> 
Sorry, I mean, I have *NOT*.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34023

[Bug c++/34023] Wrong using of user-defined conversion operator for converting rvalue to reference on constant.

[sergey dot gcc at comrades dot id dot au]

------- Comment #3 from sergey dot gcc at comrades dot id dot au  2007-11-09 01:14 -------
// Workaround:
class a
{
public:
        template<class T>
        operator T &() const
                throw(typename ::boost::disable_if<
                        ::boost::is_same<T, ref_t const> >::type *)
        {
                static int f;
                return f;
        }
};

int main()
{
        a const &aa = a(); // line # 27
        int &i = aa;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34023

[Bug c++/34023] Wrong using of user-defined conversion operator for converting rvalue to reference on constant.

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2007-11-19 04:15 -------
This works on the trunk.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34023

[Bug c++/34023] Wrong using of user-defined conversion operator for converting rvalue to reference on constant.

[sergey dot gcc at comrades dot id dot au]

------- Comment #5 from sergey dot gcc at comrades dot id dot au  2007-11-29 00:04 -------
(In reply to comment #3)
> // Workaround:
> class a
> {
> public:
>         template<class T>
>         operator T &() const
>                 throw(typename ::boost::disable_if<
>                         ::boost::is_same<T, ref_t const> >::type *)
>         {
>                 static int f;
>                 return f;
>         }
> };
> 
> int main()
> {
>         a const &aa = a(); // line # 27
>         int &i = aa;
> }
> 

This workaround should not work, according to the standard

14.8.2.2

    - All references in the function type of the function template to the
corresponding template parameters are replaced by the specified template
argument values. If a substitution in a template parameter or in the function
type of the function template results in an invalid type, type deduction fails.
[Note: The equivalent substitution in exception specifications is done only
when the function is instantiated, at which point a program is ill-formed if
the substitution results in an invalid type.] Type deduction may fail for the
following reasons:

However, it works on GCC. It is another bug in GCC.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34023

[Bug c++/34023] Wrong using of user-defined conversion operator for converting rvalue to reference on constant.

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34023

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|gcc-bugs at gcc dot gnu.org |
         Resolution|                            |FIXED

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-25 21:59:20 UTC ---
Fixed long ago.