スーパートレイト

Rustには“継承“はありませんが、あるトレイトを別のトレイトの上位集合として定義できます。例えば：

trait Person {
    fn name(&self) -> String;
}

// PersonはStudentのスーパートレイトです。
// Studentを実装するにはPersonも実装する必要があります。
trait Student: Person {
    fn university(&self) -> String;
}

trait Programmer {
    fn fav_language(&self) -> String;
}

// CompSciStudent (computer science student) is a subtrait of both Programmer
// and Student. Implementing CompSciStudent requires you to impl both supertraits.
trait CompSciStudent: Programmer + Student {
    fn git_username(&self) -> String;
}

fn comp_sci_student_greeting(student: &dyn CompSciStudent) -> String {
    format!(
        "My name is {} and I attend {}. My favorite language is {}. My Git username is {}",
        student.name(),
        student.university(),
        student.fav_language(),
        student.git_username()
    )
}

struct CSStudent {
    name: String,
    university: String,
    fav_language: String,
    git_username: String
}

impl Programmer for CSStudent {
    fn fav_language(&self) -> String {
        self.fav_language.clone()
    }
}

impl Student for CSStudent {
    fn university(&self) -> String {
        self.university.clone()
    }
}

impl Person for CSStudent {
    fn name(&self) -> String {
        self.name.clone()
    }
}

impl CompSciStudent for CSStudent {
    fn git_username(&self) -> String {
        self.git_username.clone()
    }
}

fn main() {
    let student = CSStudent {
        name: String::from("Alice"),
        university: String::from("MIT"),
        fav_language: String::from("Rust"),
        git_username: String::from("alice_codes"),
    };

    let greeting = comp_sci_student_greeting(&student);
    println!("{}", greeting);
}

参照

The Rust Programming Language chapter on supertraits