src/trait/supertraits.md

# Supertraits

Rust doesn't have "inheritance", but you can define a trait as being a superset
of another trait. For example:

```rust,editable
trait Person {
    fn name(&self) -> String;
}

// Person is a supertrait of Student.
// Implementing Student requires you to also impl Person.
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);
}
```

### See also:

[The Rust Programming Language chapter on supertraits][trpl_supertraits]

[trpl_supertraits]: https://doc.rust-lang.org/book/ch19-03-advanced-traits.html#using-supertraits-to-require-one-traits-functionality-within-another-trait