sealed top-level constant Null safety

_Sealed const sealed

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 C, and C and D are declared in different packages.

Implementation

const _Sealed sealed = _Sealed();