[_y5hn]

Maybe he meant something similar to Go interfaces, but they are abstract and coupled loosely with implementations after the fact.

That or abstract class/pure interface. There's no need for default implementations introducing assumptions in code.

[rectang]

I believe that both Go and Rust use two-word fat pointers for interface types. I was actually thinking of Rust traits first and foremost; in Rust, traits can supply default method implementations which invoke other methods defined in the same trait.

While I take your point about introducing assumptions, I'm reluctant to give up the convenience of default implementations; they seem to present fewer problems than classically inherited methods because shallow hierarchies are more common with interfaces than with classical inheritance, and because default interface methods cannot directly access member variables because they do not know about object layout — unlike methods inherited from a parent class under classical inheritance.

[ratww]

"Interfaces with default implementations" are a thing in Java and in some other languages, but most people don't know about them:

https://docs.oracle.com/javase/tutorial/java/IandI/defaultme...

[rectang]

I knew that Java added "default methods" to its interfaces a few years ago, but wasn't sure whether Java uses "fat pointers" like Rust and Go.