Dart doesn't allow final class

[dev-aentgs]

Description:
Effective dart guidelines mention the following.
AVOID extending a class that isn’t intended to be subclassed.

Like in java, in this case allowing the class to be marked as final would prevent another class from inheriting it, dart doesn't allow final class.
What would be the side effects if this was allowed?
Would this be a breaking change?

effective dart #2440

[srawlins]

We do have a @sealed annotation for the present. But it's not a hard language feature, just for static analysis.

#349 is a related issue.

[Cat-sushi]

see also #11

[kevmoo]

See proposed solution at #704

[srawlins]

This can be closed; we now have final classes.