structural typing? duck typing?
duck typing is what ruby does without sorbet or rbs, it portrays nothing about how the code bits interact at the boundary. if a "dog" is passed in but a "cat" is expected, things will work just fine until runtime when the cat is asked to bark. (saying as someone who is a big fan of ruby overall)
It is developer responsibility to ensure that you will not receive cat during designing stage of your classes. And inheritance is bad, this is also sharp knife. But annotating everywhere
sig { params(cat: Cat) }