On Oct 9, 2019, at 2:26 PM, Brian Goetz <brian.go...@oracle.com> wrote: > > It is allowable, though somewhat silly, to put the `final` modifier on local > classes. > > From a hierarchy-protection point of view, allowing local classes to be > `sealed` is also silly, as it cannot be extended from outside the method > anyway, and even if it could, such types can't show up in APIs that are > accessible from outside. > > From an exhaustiveness point of view, though, one can imagine having a sealed > local hierarchy (sum of records) that will be switched over within the > method, though one would have to work pretty hard to imagine that. > > Note that a local class cannot be a subtype of a sealed type declared outside > the same method (*), since it can't be denoted in the permits clause. > > (*) unless the permits clause is inferred. Yuck. Now a mangled name would > go into the PermittedSubtypes attribute. > > Proposal: ban `sealed` and `non-sealed` modifiers on _local_ classes and > interfaces.
I’m OK with that ban as a starting position at least. We can lift it later if we need to. It’s a little like the ban on statics: You can’t cut arbitrary class structure into an arbitrary block.
