That's a question of API, not type system.

It's only enforced because of Rust's strict type system. Python, on the other hand, lets you do whatever you want by comparison, and complains only at runtime. I've seen far too many **kwargs for my liking.

And FD types (e.g. OwnedFd, BorrowedFd) are already in std.

My example would be a thin wrapper around these, most likely. It's only an example of what I'm trying to convey, though.