Certainly a safe interface is better than none, but unsafe and/or inefficient implementations are just symptoms of expressiveness issues, not a fact of life. Th

Certainly a safe interface is better than none, but unsafe and/or inefficient implementations are just symptoms of expressiveness issues, not a fact of life. That being said, what Rust has is already a strict improvement over not even being able to state how ephemeral data structures can be safely used. Also, establishing the safety of code that manipulates arrays (without runtime bounds checks), cyclical data structures (e.g. doubly-linked lists) and user-defined forms of indirection (e.g. hashing) is probably best done using tools other than unification-based type checkers.