> Making opt-in explicit effectively solves this problem. It is clearly written out which traits a type is expected to fulfill, and if the type is changed in such a way as to violate one of these traits, an error will be reported at the impl site (or #[deriving] declaration).
Please implement this RFC. I really hope this gets in before Rust 1.0. I'm extremely excited and looking forward to using Rust in all my hobby projects once it stabilizes, but honestly when going through the tutorial this stood out as the only ugly wart in an otherwise amazingly beautiful language.