are abstract / base specifiers permitted or required on class forward declarations?

[zygoloid]

Summary of issue:

Given this class:

base class C {}

how does one write a forward declaration? Is

base class C;

valid? Is

class C;

valid?

Details:

There doesn't seem to be a reason to require the abstract or base specifier to be present on a forward declaration. But usually our forward declaration syntax for classes is a prefix of the definition, and there also doesn't seem to be any particular hardship to developers in requiring the forward declaration to repeat the specifier.

In addition to the three answers suggested by the question (specifier is disallowed, specifier is allowed but not required, specifier is required), we could change the class definition syntax to put the specifier in the class body, as we did for inheritance:

class C {
  base class;
  extend base: B;
}

Any other information that you want to share?

No response

[chandlerc]

@justzh - Please keep comments on PRs and issues constructive and on-topic. I'm hiding yours, but you've had warnings now and so I will block if this continues.