https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100443
Bug ID: 100443
Summary: member using declaration of function templates with
different return types does not bring base class
overload into derived class
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: gonzalo.gadeschi at gmail dot com
Target Milestone: ---
GCC incorrectly accepts the following example
(https://gcc.godbolt.org/z/YWd98oGY7):
template <class T> struct A {
template <class U> long f(U) const { return 1; }
};
struct B : A<int> {
using A<int>::f;
template <class U> int f(U) const { return 2; }
};
int main() {
return B{}.f(3);
}
Instead, it should error at "B{}.f(3)", since the call is ambiguous.
A member using declaration brings into the derived class all the overloads of
the specified function from the given base class, except for any overloads
where the derived class has a function declaration with the same signature
([namespace.udecl]/p11).
For non-template functions, the return type is not part of the signature
([defns.signature.member]).
For function templates, the return type is part of the signature
([defns.signature.member.templ]).
In this example, A<int>::f and B::f have different return types (long vs int),
and have different signatures. B::f does not hide A<int>::f, and both B::f and
A<int>::f are available for overload resolution.
Because they have the same parameters types, any call is ambiguous.
