Rust by Example

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()

)

}

fn main() {}

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See also:

The Rust Programming Language chapter on supertraits

Disambiguating overlapping traits

A type can implement many different traits. What if two traits both require the same name? For example, many traits might have a method named get(). They might even have different return types!

Good news: because each trait implementation gets its own impl block, it's clear which trait's get method you're implementing.

What about when it comes time to call those methods? To disambiguate between them, we have to use Fully Qualified Syntax.

trait UsernameWidget {

// Get the selected username out of this widget

fn get(&self) -> String;

}

trait AgeWidget {

// Get the selected age out of this widget

fn get(&self) -> u8;

}

// A form with both a UsernameWidget and an AgeWidget

struct Form {

username: String,

age: u8,

}

impl UsernameWidget for Form {

fn get(&self) -> String {

self.username.clone()

}

}

impl AgeWidget for Form {

fn get(&self) -> u8 {

self.age

}

}

fn main() {

let form = Form{

username: "rustacean".to_owned(),

age: 28,

};

// If you uncomment this line, you'll get an error saying

// "multiple `get` found". Because, after all, there are multiple methods

// named `get`.

// println!("{}", form.get());

let username =

::get(&form);

assert_eq!("rustacean".to_owned(), username);

let age =

::get(&form);

assert_eq!(28, age);

}

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