> It's perfectly clear to a human that this code is fine and doesn't have any actual ownership issues. I think there's another part of the story in a few of th

> It's perfectly clear to a human that this code is fine and doesn't have any actual ownership issues. I think there's another part of the story in a few of these examples that the author might be missing. Sometimes Rust doesn't want to infer/allow things because of the Halting Problem or whatever, but other times it's because that inference would amount to a compatibility hazard that the user might not've realized they were creating. "Types implement `Copy` automatically" is a good example of one of these. It would be an easy rule to implement (and it is in fact how `Send` and `Sync` and some other things work), but it would also mean that adding a non-Copy private field to a struct that didn't previously have one could break callers. I wouldn't call it a slam-dunk case for the rules being what they are -- and you could argue that it prioritizes the needs of library code over the needs of application code -- but anyway it's some context.