Expand description
Define an alias for an existing type.
The syntax is type Name = ExistingType;.
Examples
type does not create a new type:
type Meters = u32;
type Kilograms = u32;
let m: Meters = 3;
let k: Kilograms = 3;
assert_eq!(m, k);A type can be generic:
type ArcMutex<T> = Arc<Mutex<T>>;In traits, type is used to declare an associated type:
trait Iterator {
    // associated type declaration
    type Item;
    fn next(&mut self) -> Option<Self::Item>;
}
struct Once<T>(Option<T>);
impl<T> Iterator for Once<T> {
    // associated type definition
    type Item = T;
    fn next(&mut self) -> Option<Self::Item> {
        self.0.take()
    }
}