comprehensive-rust/src/generics/trait-bounds.md

Trait Bounds

When working with generics, you often want to limit the types. You can do this with T: Trait or impl Trait:

fn duplicate<T: Clone>(a: T) -> (T, T) {
    (a.clone(), a.clone())
}

// struct NotClonable;

fn main() {
    let foo = String::from("foo");
    let pair = duplicate(foo);
}

Consider showing a where clause syntax. Students can encounter it too when reading code.

fn duplicate<T>(a: T) -> (T, T)
where
    T: Clone,
{
    (a.clone(), a.clone())
}

• It declutters the function signature if you have many parameters.
• It has additional features making it more powerful.
  • If someone asks, the extra feature is that the type on the left of ":" can be arbitrary, like Option<T>.