https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103084
--- Comment #8 from Aaron Ballman <aaron at aaronballman dot com> --- (In reply to M Welinder from comment #6) > elaborated-enum-specifier can be a elaborated-type-specifier. It is in the > "enum Hog H;" case. > > But elaborated-enum-specifier is NOT an elaborated-type-specifier in the > "using enum Hog;" case, > > See http://eel.is/c++draft/enum.udecl -- this uses elaborated-enum-specifier > directly. You're correct about the productions, but http://eel.is/c++draft/dcl.type.elab then provides no semantics whatsoever for what type is referred to by an elaborated-enum-specifier. https://eel.is/c++draft/dcl.type.elab#6 would not apply, so the only requirement on the type then comes from http://eel.is/c++draft/enum.udecl#1, which says that the type referred to must be a reachable enum-specifier. But the type named isn't a reachable enum-specifier (maybe, who knows, no semantics means we can't really say), it's a type alias to an enum-specifier. So there's confusion either way you read it, IMO. (In reply to M Welinder from comment #7) > Maybe kick it up to the C++ people? > > Note, that if the code is not allowed then a type alias is no longer as > powerful as the original type. I really doubt that was intended. FWIW, my initial inclination was that Clang and ICC were wrong to reject because this does seem like a useful construct that should be supported. It is possible there's a Core issue here and that this should not be rejected. The original paper on the topic doesn't say anything, and I didn't see a mention of type aliases in the WG21 wiki discussions for the paper, but it's entirely possible I missed something while looking. So I agree that it'd be useful to allow this, but I'm not convinced the standard permits it currently.
