Structural typing has the benefit of making it easier to code to an interface and reminds me of Go. If you have a function that requires a method off a class (say, `poop`), then rather than declaring it to accept `Cat | Dog` (or overload it, in e.g. Java), you code it to accept an object with a single function (`pooper: { poop: VoidFunction}`). Then anything that implements it can use it, testing is typed and easy, and changing the class is less likely to affect the consuming method.

Its such a powerful pattern, I'm a bit surprised to see so much negativity about it. I'm aware there's alternatives and reasoned opinions, but I bet a significant number of people have never seen or programmed in this style and aren't aware of what they are missing. For me, I can't imagine using another typed language that doesn't support implicit interfaces in this manner.