Your comment is incoherent. First, it applies so long as a type system is an effective tool at telling you this, and so long as that tool is not completely (or

Your comment is incoherent. First, it applies so long as a type system is an effective tool at telling you this, and so long as that tool is not completely (or at least substantially) supplanted by other tools. In no way does it have to be "the only tool" - there are lots of tools I find useful to tell me when things are going wrong in my code: types, tests, assertions, linting. Even with the other three, types cover meaningful territory. Second, as you half note, the system you describe would be a type system (and sounds somewhat similar to core.typed in clojure, though my understanding thereof is tremendously superficial). The rest of your comment just seems not to follow. Type systems aren't silver bullets for keeping agility in the face of changes, in the same way that hammers aren't silver bullets for driving nails. You can use them wrong, you can hurt yourself, but you sure want one (... but probably not the weird shaped one with a loose head over there labeled "Java"...).