Why does Kotlin prohibit exposing restricted-visibility types?

[tieskedh]

I think this question is roughly the same as:

Non-public Interface members

I believe protected and internal interface members is an underestimated feature modern languages have to support. And here I’ll explain why I believe so. Let’s scrutinize some use cases: A general-use interface like Runnable. It’s widely used by a variety of frameworks and end-user code. It’s usually implemented by small objects with limited functionality and scope of usage. It’s the case when the statement “an interface is a public contract between the caller and a callee” is relevant. So t…