literally
macro_rules! hset { (@single $($x:tt)*) => { ... }; (@count $($rest:expr),*) => { ... }; ($($key:expr,)+) => { ... }; ($($key:expr),*) => { ... }; }
Literally just a HashSet literal with values into'd.
let s: HashSet<String> = hset!{ "value" }; assert_eq!(s.get("value"), Some(&"value".to_string()))