[Bug c++/49458] New: [C++0x] Obvious candidate for conversion to function lvalue rejected

["hstong at ca dot ibm.com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49458

           Summary: [C++0x] Obvious candidate for conversion to function
                    lvalue rejected
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: hstong@ca.ibm.com
                CC: michaelw@ca.ibm.com
              Host: powerpc64-unknown-linux-gnu
            Target: powerpc64-unknown-linux-gnu


According to the 2011 FCD, subclause 13.3.1.6 [over.match.ref] paragraph 1:
>>>
The conversion functions of S and its base classes are considered, except that
for copy-initialization, only the non-explicit conversion functions are
considered. Those that are not hidden within S and yield type "lvalue reference
to cv2 T2" (when 8.5.3 requires an lvalue result) or "cv2 T2" or
"rvalue reference to cv2 T2" (when 8.5.3 requires an rvalue result), where
"cv1 T" is reference-compatible (8.5.3) with "cv2 T2", are candidate functions.
<<<

Both lvalue references and rvalue references to function types require binding
to function lvalues. The following test case is expected to compile clean.

GCC still does not compile if #1 is commented out.

GCC will compile if #2 is commented out, but that behaviour is unsupported by
the referenced wording.

In particular, #2 should be a candidate and (from the wording) #1 is not for
conversion to a function lvalue.


### Self-contained source (a.cpp):> cat a.cpp
typedef void ftype();
void foo() { }

struct A {
   operator ftype&&(void);  // #1
   operator ftype&(void) { return foo; }  // #2
};

ftype &&frvref = A();


### Compiler invocation:
g++-4.6.0 -std=c++0x -o a.o -c a.cpp


### Compiler output:
a.cpp:9:20: error: invalid initialization of reference of type âvoid (&&)()â
from expression of type âAâ


### g++ -v output:> g++-4.6.0 -v
Using built-in specs.
COLLECT_GCC=g++-4.6.0
COLLECT_LTO_WRAPPER=/data/gcc/libexec/gcc/powerpc64-unknown-linux-gnu/4.6.0/lto-wrapper
Target: powerpc64-unknown-linux-gnu
Configured with: ./configure --prefix=/data/gcc --program-suffix=-4.6.0
--disable-libssp --disable-libgcj --enable-version-specific-runtime-libs
--with-cpu=default32 --enable-secureplt --with-long-double-128 --enable-shared
--enable-__cxa_atexit --enable-threads=posix --enable-languages=c,c++,fortran
--with-gmp=/usr/local
Thread model: posix
gcc version 4.6.0 (GCC)