[Bug c++/46687] Class member lookup ambiguity w/ overloaded static members and using declarations

[fabien at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46687

fabien at gcc dot gnu.org changed:

   What|Removed |Added

 Status|UNCONFIRMED |ASSIGNED
   Last reconfirmed||2012-09-02
 Ever Confirmed|0   |1

[Bug c++/46687] Class member lookup ambiguity w/ overloaded static members and using declarations

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46687

--- Comment #1 from Jonathan Wakely redi at gcc dot gnu.org 2010-11-28 
01:43:26 UTC ---
why do you think it's not ambiguous?

C has two bases of type A, so two copies of A::foo()

[Bug c++/46687] Class member lookup ambiguity w/ overloaded static members and using declarations

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46687

--- Comment #2 from Jonathan Wakely redi at gcc dot gnu.org 2010-11-28 
01:57:06 UTC ---
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

[Bug c++/46687] Class member lookup ambiguity w/ overloaded static members and using declarations

[hstong at ca dot ibm.com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46687

--- Comment #3 from Hubert Tong hstong at ca dot ibm.com 2010-11-28 04:23:55 
UTC ---
(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.