[AnimalMuppet]

In your view, how is "interfaces with default implementations" different from "inheritance for code reuse"? At a minimum it looks like a virtual function with a default implementation in the base class. If a derived class doesn't override it, isn't that code reuse?

[rectang]

> In your view, how is "interfaces with default implementations" different from "inheritance for code reuse"?

The latter is a more general classification?

A type which inherits a default method implementation from an interface is an example of "inheritance for code reuse".

A type which inherits a method implementation from a parent class under classical OOP is also an example of "inheritance for code reuse".

However, I argue that "interface inheritance with default implementations" is superior to "classical OOP" because it avoids tight coupling with memory layout, problems with implementing multiple inheritance in classical OOP, etc.

[_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.

[Spivak]

Because interfaces don’t confer a relationship between implementations, only that they have some common method signatures.

[username90]

> Because interfaces don’t confer a relationship between implementations

Having the interface implement functions does exactly that, so your point only applies for interfaces without implementations.