According to cppreference, both gcc and msvc have completed the implementation of C++20 feature using enum
, which means we can using-declaration with an enum
:
struct A {
enum e { /* ... */ };
};
struct S {
using enum A::e;
};
But when I apply it to the templates:
template <class T>
struct S {
using enum T::e;
};
gcc rejects it with:
<source>:7:14: error: 'using enum' of dependent type 'typename T::e'
7 | using enum T::e;
| ^~~~
<source>:7:17: note: declared here
7 | using enum T::e;
| ^
msvc also rejects it with:
<source>(7): error C2868: 'e': ill-formed using-declaration; expected a qualified-name
<source>(8): note: see reference to class template instantiation 'S<T>' being compiled
I have no idea why this cannot work since it seems to be no different from non-templates.
Is this a compiler bug or just ill-formed?
From the proposal:
The elaborated-enum-specifier shall not name a dependent type and the type shall have a reachable enum-specifier.
In your example T::e
is a dependent type.