Mastering Rust - Second Edition

Using + to compose traits as bounds

We can also specify multiple trait bounds to a generic type using the + symbol. Let's take a look at the impl block for the HashMap type from the standard library:

impl<K: Hash + Eq, V> HashMap<K, V, RandomState>

Here, we can see that K, denoting the type of the HashMap key, has to implement the Eq trait, as well as the Hash trait.

We can also combine traits to create a new trait, that represents all of them:

// traits_composition.rstrait Eat {    fn eat(&self) {        println!("eat");    }}trait Code {    fn code(&self) {        println!("code");    }}trait Sleep {    fn sleep(&self) {        println!("sleep");    }}trait Programmer : Eat + Code + Sleep {    fn animate(&self) {        self.eat();        self.code();        self.sleep();        println!("repeat!");    }}struct ...