closed class / open
Also written: open, open class, closed
A normal class is closed, so nobody can extend it. Marking it `open` lets other classes build on it, and marking a function `open` lets a subclass override it.
Also written: open, open class, closed
A normal class is closed, so nobody can extend it. Marking it `open` lets other classes build on it, and marking a function `open` lets a subclass override it.