[swift-evolution] [swift-evolution-announce] [Review #2] SE-0117: Default classes to be non-subclassable publicly

[Garth Snyder]

> Károly wrote: I suggest we change the proposal to remove the implicit "sealed" level of public member overridability, and support only "open" or "final" class members. For members, "open" should mean the opposite of "final", with no levels in between. Member-level openness should be entirely independent of visibility; so it should be possible to say "internal open" to mean an internally overridable member that's not at all visible outside the module -- the same as today's default.

What is the distinction between this approach and simply omitting the ability to apply the “open” keyword to anything but a class?

The current behavior is (IIUC) that you cannot override a superclass’s final method. Aside from that, you can override any other method that’s visible to you, wherever you stand with regard to the superclass’s origin. If there’s no sealed status for members, why is any change to member annotations needed at all?

Garth