Make it an error to have on F when F is final in another library.
#2956
Conversation
A little rephrasing and refactoring to the rules, but that's the only intended change. The structure of the restrictions on other libraries are now: * Sealed - cannot subtype, no exceptions * Final - cannot subtype, SDK exceptions. * Interface - cannot extend/with, SDK exceptions * Base/Final - transitively cannot implement, SDK exception. Also same library: * Base/Final - transitively must be base/final/sealed. No exceptions.
| More formally, it's a compile-time error if: | ||
| A `class`, `mixin class`, `mixin` or `enum` declaration from library *L* | ||
| has a direct superdeclaration *S* marked `final` _(so necessarily a `class` | ||
| declaration)_ in a library *K*, neither: |
There was a problem hiding this comment.
I would do "neither" -> "and neither of the following is true".
And then remove the "nor," from the first bullet.
Likewise further below.
| from another library _(with some exceptions for platform libraries)_. | ||
| _(You cannot inherit implementation from a class marked `interface` | ||
| or `final` except inside the same library. Unless you are in a |
There was a problem hiding this comment.
Maybe remove the final-related example on lines 599 and 705 if we aren't talking about it in this section anymore.
| More formally, it's a compile-time error if: | ||
| A `class`, `mixin-class`, `mixin` or `enum` declaration in library *L* has | ||
| a declared interface *P*, and *P* has any superdeclaration *S*, | ||
| from a library *K*, which is marked `base` or `final` |
There was a problem hiding this comment.
Also, since you specify behaviour for final declaration subtyping on line 683, maybe move these final examples (that aren't already in the final section) over to there and remove talking about both base and final in this section?
It's nice to read about each modifier one at a time.
There was a problem hiding this comment.
This rule might just be about base, because it's impossible to have a super-declaration marked final in another library without also having a super-declaration marked base in that other library, because that's the only possible way to have a direct super-declaration from that library with the final declaration as super-declaration.
(I think. It's always worrisome to define rules that depend on other rules to be complete. If we remove or tweak the other rule, then this rule might start allowing something we didn't intend.
So, be complete in every rule, as if it was stand-alone, or be minimal and non-redundant? I'm aiming for the former.)
Disallows a
mixindeclaration to have an other-libraryfinaltype asontype.A little rephrasing and refactoring to the rules, but that's the only intended change,
anything else is intended as clarification.
The structure of the restrictions on other libraries are now:
Also same library: