https://blog.rust-lang.org/2018/05/10/Rust-1.26.html "At long last, impl Trait is here! This feature has been highly desired for quite a while, and provides a feature known as “existential types.” It’s simpler than that sounds, however. The core of it is this idea: ... Speaking of papercuts, since Rust uses the Result type for returning errors, and ? to make handling them easy, a common pain-point of new Rustaceans is to try and use ? in main: ... Inclusive ranges with ..= ... Another long-awaited feature is “slice patterns.” These let you match on slices similar to how you match on other data types."