typeMeters = u32;typeKilograms = u32;letm: Meters =3;letk: Kilograms =3;assert_eq!(m, k);

typeArcMutex<T> = Arc<Mutex<T>>;

traitIterator {// associated type declarationtypeItem;fnnext(&mutself) ->Option<Self::Item>;}structOnce<T>(Option<T>);impl<T> IteratorforOnce<T> {// associated type definitiontypeItem = T;fnnext(&mutself) ->Option<Self::Item> {self.0.take()    }}