Comment by rezonant

Yes, Crystal is not a superset of Ruby with all of its behaviors and semantics. And thus, it is great if you are starting fresh and don't mind foregoing the Ruby gem ecosystem and the popular frameworks like Rails proper.

But it's not a migration path for Ruby codebases to add types, like the new initiatives for type annotations are. It's just that the syntax used by the available options has been somewhere between bad and downright terrifying until now.