In the test case below, there is a set of overloaded static member functions foo() whose true declarations all come from struct A. While lookup from C would find foo in both B1 and B2, B1::foo refers to the same set of entities as B2::foo. There should be no ambiguity; GCC reports otherwise. The overload candidates for foo should be unambiguously found on the call and overload resolution should determine that foo(void) is being called. I also find it odd that the candidates are listed three times. ### Self-contained source (dataa.cpp): struct A { static int foo(); static int foo(char); }; struct B1 : A { using A::foo; }; struct B2 : A { using A::foo; }; struct C : B1, B2 { }; enum { X = sizeof C::foo() }; ### Command to reproduce: g++ -c dataa.cpp ### Compiler output: dataa.cpp:11:19: error: reference to 'foo' is ambiguous dataa.cpp:3:15: error: candidates are: static int A::foo(char) dataa.cpp:2:15: error: static int A::foo() dataa.cpp:2:15: error: static int A::foo() dataa.cpp:3:15: error: static int A::foo(char) dataa.cpp:2:15: error: static int A::foo() dataa.cpp:3:15: error: static int A::foo(char) ### g++ -v output: Using built-in specs. Target: powerpc64-unknown-linux-gnu Configured with: ../gcc-4.5.0/configure --prefix=/data/gcc --program-suffix=-4.5.0 --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 Thread model: posix GNU C++ (GCC) version 4.5.0 (powerpc64-unknown-linux-gnu)
why do you think it's not ambiguous? C has two bases of type A, so two copies of A::foo()
C has two copies of the name A::foo, as B1::foo and B2::foo. if C only saw A::foo then it would be unambiguous because the same members would be found, as in this variant: struct A { static int foo(); static int foo(char); }; struct B1 : A { }; struct B2 : A { }; struct C : B1, B2 { }; enum { X = sizeof C::foo() }; However, because you have using declarations in B1 and B2 name lookup finds B1::foo and B2::foo ... at least by my reading, which could be wrong
(In reply to comment #2) > However, because you have using declarations in B1 and B2 name lookup finds > B1::foo and B2::foo ... at least by my reading, which could be wrong It does find B1::foo and B2::foo, but then again, B1::foo and B2::foo refer to the same functions. In the N3126 wording, the declaration sets for looking up B1::foo and B2::foo are the same. I believe the case presented is valid under both the C++03 and the N3126 wording. >>> C++03 subclause 10.2 [class.member.lookup] paragraph 2: First, every declaration for the name in the class and in each of its base class sub-objects is considered. ... Each of these declarations that was introduced by a using-declaration is considered to be from each sub-object of C that is of the type containing the declaration designated by the using-declaration. If the resulting set of declarations are not all from sub-objects of the same type, or the set has a nonstatic member and includes members from distinct sub-objects, there is an ambiguity and the program is ill-formed. Otherwise that set is the result of the lookup. <<< My understanding is that the resulting set of declarations are all from subobjects of the same type (the two subobjects, C::B1::A and C::B2::A) and the set has no nonstatic members (all functions foo() are static member functions). From this paragraph, we have a set of declarations as the result of lookup: { ::A::foo(void), ::A::foo(char) } Overload resolution then takes place.