I don’t use extensions, even convenient ones, as I have to be able to run my code on a variety of compilers. If you don’t have to do that, some extensions (like this one) are really handy.
> An unnamed enumeration that does not have a typedef name for linkage purposes ([dcl.typedef]) and that has a first enumerator is denoted, for linkage purposes ([basic.link]), by its underlying type and its first enumerator; such an enumeration is said to have an enumerator as a name for linkage purposes.
And for classes/structs, [class.pre](https://eel.is/c++draft/class.pre#def:class,unnamed) has explicit wording:
> A class-specifier whose class-head omits the class-head-name defines an unnamed class.
So both are entirely fine (and likewise, unions are too).
Note that my links are for the current draft, but I just checked and this was already the case as far back as C++11. So I wonder where this persistent myth seems to come from.
The part of enums you quoted was C-compatible enums; anonymous scoped enums are explicitly forbidden: "The optional enum-head-name shall not be omitted in the declaration of a scoped enumeration" (dcl.enum 2).
Sigh. I will send in a clarification at least on the class/struct/union side. Ideally the grammar would be fixed rather than that paragraph.
The draft I looked at is https://timsong-cpp.github.io/cppwp/n4868/ (2020-10-18, shortly after the standard was approved).
