[Bug c++/33409] New: Overload Resolution Succeeds When Actually Ambiguous.

[martinezfive at comcast dot net]

With the following command line:
[c:\hack]==► gcc -v -save-temps --pedantic -c a.cpp
Reading specs from /mingw/lib/gcc/mingw32/3.4.2/specs
Configured with: ../gcc/configure --with-gcc --with-gnu-ld --with-gnu-as
--host=mingw32 --target=mingw32 --prefix=/mingw --enable-threads --disable-nls
--enable-languages=c,c++,f77,ada,objc,java --disable-win32-registry
--disable-shared --enable-sjlj-exceptions --enable-libgcj --disable-java-awt
--without-x --enable-java-gc=boehm --disable-libgcj-debug --enable-interpreter
--enable-hash-synchronization --enable-libstdcxx-debug
Thread model: win32
gcc version 3.4.2 (mingw-special)
 cc1plus -E -quiet -v -iprefix ../lib/gcc/mingw32/3.4.2/ a.cpp -pedantic -o
a.ii

ignoring nonexistent directory
"../lib/gcc/mingw32/3.4.2/../../../../include/c++/3.4.2"
ignoring nonexistent directory
"../lib/gcc/mingw32/3.4.2/../../../../include/c++/3.4.2/mingw32"
ignoring nonexistent directory
"../lib/gcc/mingw32/3.4.2/../../../../include/c++/3.4.2/backward"
ignoring nonexistent directory "../lib/gcc/mingw32/3.4.2/../../../../include"
ignoring nonexistent directory "../lib/gcc/mingw32/3.4.2/include"
ignoring nonexistent directory
"../lib/gcc/mingw32/3.4.2/../../../../mingw32/include"
ignoring nonexistent directory "/mingw/mingw32/include"
#include "..." search starts here:
#include <...> search starts here:
 /mingw/include/c++/3.4.2
 /mingw/include/c++/3.4.2/mingw32
 /mingw/include/c++/3.4.2/backward
 /mingw/include
 /mingw/include
 /mingw/lib/gcc/mingw32/3.4.2/include
 /mingw/include
End of search list.
 cc1plus -fpreprocessed a.ii -quiet -dumpbase a.cpp -auxbase a -pedantic
-version -o a.s
GNU C++ version 3.4.2 (mingw-special) (mingw32)
        compiled by GNU C version 3.4.2 (mingw-special).
GGC heuristics: --param ggc-min-expand=99 --param ggc-min-heapsize=130924 as -o
a.o a.s

where a.cpp contains the following:
class A
    {
  public:
    A( double );
    operator long();
    };

A  operator% ( const A&, const A& );

void x()
    {
    A g(0);
    double d = 1.2;
    d = d % g; //Should report on ambiguous call
    }

I get no complaint from gcc.  However, the call is ambiguous according to the
ISO C++ 2003 Standard.  The rationale follows:

   1. The candidate functions are a) operator%(const A &, const A &) and b)
built-in operator % (arguments: both integral/enumeration)
   2. Both candidates has the same # of parameters.
   3. Implicit conversion sequences for each argument:
          double->const A via copy-initializing a temporary const A
          A->const A, Exact Match via reference binding and Qualification
Adjustment
          double->integral/enumeration via floating-integral conversion
          A->long via the User-Defined Conversion Sequence of Identity
Conversion->A::operator long() invocation->Identity Conversion
   4. ICS1(non built-in): User-Defined Conversion Sequence
      ICS2(non built-in): Qualification Adjustment
      ICS1(built-in): Floating-integral conversion
      ICS2(built-in): User-Defined Conversion Sequence
   5. By 13.3.3.2,
          ICS2(non built-in) represents a "better conversion sequence" than
ICS2(built-in): Standard v. User-Defined
          ICS1(non built-in) represents a "worse conversion sequence" than
ICS1(built-in): User-Defined v. Standard

Therefore, neither operator invocation constitutes a "best viable function" and
the program is ill-formed.

I ran this by the people at EDG and received a reply agreeing with my analysis.


-- 
           Summary: Overload Resolution Succeeds When Actually Ambiguous.
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: martinezfive at comcast dot net


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33409