The following code does not compile:
------------------templcvt.cc----------------
extern int f( int ) ;
class B
{
public:
template< typename T >
operator T const& () const
{
return f( 42 ) ;
}
} ;
B
g()
{
return B() ;
}
---------------------------------------------
When invoking "g++ -c templcvt.cc", the compiler outputs the
following error messages:
templcvt.cc: In member function 'B::operator const T&() const [with T =
B]':
templcvt.cc:24: instantiated from here
templcvt.cc:17: error: invalid initialization of reference of type 'const
B&' from expression of type 'int'
Apparently, it is instantiating the template conversion operator
in order to bind the temporary object to the B const& argument
of the (implicit) copy constructor. This dispite §12.3.2.1 "A
conversion function is never used to convert a (possibly
cv-qualified) object to the (possibly cv-qualified) same object
type (or a reference to it),[...]" (and the fact, of course,
that a function template should only be instantiated if the
function is used).
There's a simple work-around: just define an explicit:
operator B const&() const { return *this ; }
as well. But this shouldn't be necessary.
(See also the discussion in comp.std.c++:
http://groups.google.com/group/comp.std.c++/browse_frm/thread/32139b794c433839/#)
--
Summary: template user defined conversion operator instantiated
for conversion to self
Product: gcc
Version: 4.1.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: james dot kanze at gmail dot com
GCC build triplet: x86_64-unknown-linux-gnu
GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31419
