I'd go one further and say that the way other languages do it does a better job of letting you define interfaces for types you don't control. Sometimes the type

I'd go one further and say that the way other languages do it does a better job of letting you define interfaces for types you don't control. Sometimes the type you want to apply your interface/trait to doesn't have a function that does what you need, but could easily be assembled from other members of the type. And sometimes it does have a function that would work, except that the name is different. There's an Uncle Bob talk I watched a while back where he suggests that oftentimes language designers will say just about anything to avoid admitting that the real reason a feature is absent or was implemented in a hacky way is for the convenience of the compiler's authors.