On 5/12/26 13:48, Yongwei Wu via Std-Discussion wrote:
> Actually, if we change
>
> struct Derived : public Middle { public: using ::Base::member; };
>
> to
>
> struct Derived : public Middle { public: using Base::member; };
>
> Clang will reject the code. So it seems to me that Clang is applying
> different rules to the type identification and the using declaration.
> But [namespace.udecl]/3 <https://eel.is/c++draft/namespace.udecl#3>
> says each using-declarator shall either name an enumerator or have a
> nested-name-specifier naming a base class of the current class.
>
> So now I think Clang is simply confused and this is a bug.

My reading would be: <https://eel.is/c++draft/namespace.udecl#3>
requires that the nested-name-specifier names a base class, which is the
case for both `::Base` and `Base`. And
<https://eel.is/c++draft/namespace.udecl#14> requires that the named
declaration is accessible, which `::Base::member` is but `Base::member`
is not.

> On Tue, 12 May 2026 at 01:44, Anoop Rana via Std-Discussion <std-
> discussion_at_[hidden] <mailto:std-discussion_at_[hidden]>> wrote:
>
> Looks like namespace.udecl#14 <https://eel.is/c++draft/
> namespace.udecl#14> makes this ill-formed.
>
> On Mon, 11 May 2026 at 23:04, Brian Bi via Std-Discussion <std-
> discussion_at_[hidden] <mailto:std-
> discussion_at_[hidden]>> wrote:
>
> I think it's valid per the wording of the standard. Per
> [class.access.base]/5 <https://eel.is/c++draft/
> class.access.base#5>, the designating class is `Base`, and the
> member we are trying to access is public when considered as a
> member of that designating class, therefore access is granted.
>
> It does seem to me like this shouldn't be valid, and I'm not
> sure if we have the wording to make it so. Since
> [namespace.udecl]/3 <https://eel.is/c++draft/namespace.udecl#3>
> says that you must name a base class, it seems to me that there
> is some missing wording saying that it must be an accessible
> base class.
>
> That's because we treat /using-declarations/ (with the only
> exception being when they name constructors) as if they declared
> a name in a new scope that happens to refer to the same entity
> as that name in the original scope. So if we say that
> `using ::Base::member;` is valid, then we cannot stop `Derived`
> from being able to use `member` without further qualification,
> since it would then be accessing its /own/ member, not that of a
> base class. This doesn't seem like the right result, so the only
> option is to make the /using-declaration/ illegal.
>
> On Mon, May 11, 2026 at 11:31 AM Yongwei Wu via Std-Discussion
> <std-discussion_at_[hidden] <mailto:std-
> discussion_at_[hidden]>> wrote:
>
> Is the following code valid?
>
> class Base { public: int member; };
> class Middle : private Base {};
> struct Derived : public Middle { public:
> using ::Base::member; };
>
> I am inclined to think it is not valid, as :Base::member is
> not really accessible inside Derived. I believe
> accessibility is a requirement: https://eel.is/c++draft/
> namespace.udecl#14.sentence-1 <https://eel.is/c++draft/
> namespace.udecl#14.sentence-1>.
>
> However, while GCC rejects the code, both Clang and EDG
> accept it: https://godbolt.org/z/Y33drKb6n <https://
> godbolt.org/z/Y33drKb6n>.
>
> Any comments?
>
>