sealed top-level constant
Annotation marking a class as not allowed as a super-type.
Classes in the same package as the marked class may extend, implement or mix-in the annotated class.
Tools, such as the analyzer, can provide feedback if
- the annotation is associated with anything other than a class,
- the annotation is associated with a class
C, and there is a class or mixin
D, which extends, implements, mixes in, or constrains to
Dare declared in different packages.
const _Sealed sealed = const _Sealed()