https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101771
Bug ID: 101771
Summary: The keyword "typename" is illegal used in a
using-declaration that introduces the non-type
declarations
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: xmh970252187 at gmail dot com
Target Milestone: ---
struct C{
void fun(){}
};
template<class T>
struct D:T{
using typename T::fun; // #1
};
int main(){
D<C> b;
}
According to [temp.res#general-5]
>A qualified-id whose terminal name is dependent and that is in a type-only
>context is considered to denote a type. A name that refers to a
>using-declarator whose terminal name is dependent is interpreted as a
>typedef-name if the using-declarator uses the keyword typename.
`fun` in #1 is interpreted to a typedef-name
Meanwhile, according to [temp.res#general-6.5]
> The validity of a template may be checked prior to any instantiation. The
> program is ill-formed, no diagnostic required, if:
>> the interpretation of such a construct in the hypothetical instantiation is
>> different from the interpretation of the corresponding construct in any
>> actual instantiation of the template.
The actual instantiation of `D<C>` would make `fun` denotes a function rather
than denotes a type. Hence, it should be illegal.
