Comment by kaikalii

    trait Namer {
        fn first(&self) -> String;
        fn last(&self) -> String;
        // You can put this here if you want `namer.name()`
        fn name(&self) -> String {
            format!("{} {}", self.first(), self.last())
        }
    }

    fn name(n: &impl Namer) -> String {
        format!("{} {}", n.first(), n.last())
    }