[halostatue]

Ruby’s set class is implemented in Ruby wrapping a Hash (`{ key => true }`), not in C (or Java or…). It’s fairly good when you’re testing for containment, but the implementation is probably going to be as bad or worse for the #fully_contains behaviour…except the requirement that Zesty’s arrays be sorted.

Conceptually, a Set will do much better even with this sort of optimization.

[bjz_]

Interesting side-note: Rust's `HashSet<T>` is actually implemented by wrapping a `HashMap<T, ()>`. But because `()` is zero-sized (unlike a boolean), Rust can optimise a ton of stuff out.