Trait

• Traits are interfaces with extension feature in swift. trait can be implement by existing type but interfaces can't.

trait Hash {
    fn hash(&self) -> u64;
}

impl Hash for bool {
    fn hash(&self) -> u64 {
        if *self { 0 } else { 1 }
    }
}

fn test() {
    println!("{}", true.hash());
}

• Trait bound to generics.

pub fn notify(item: &impl Summary) {
    println!("Breaking news! {}", item.summarize());
}

pub fn notify<T: Summary>(item: &T) {
    println!("Breaking news! {}", item.summarize());
}

pub fn notify(item: &(impl Summary + Display)) {}

pub fn notify<T: Summary + Display>(item: &T) {}

pub fn notify<T>(item: &T) 
    where T: Summary + Display {}