Disambiguating Overlapping Traits

Introduction

In this lab, the issue of disambiguating overlapping traits is discussed, where two traits have methods with the same name and potentially different return types.

Note: If the lab does not specify a file name, you can use any file name you want. For example, you can use main.rs, compile and run it with rustc main.rs && ./main.

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 = <Form as UsernameWidget>::get(&form);
    assert_eq!("rustacean".to_owned(), username);
    let age = <Form as AgeWidget>::get(&form);
    assert_eq!(28, age);
}

Summary

Congratulations! You have completed the Disambiguating Overlapping Traits lab. You can practice more labs in LabEx to improve your skills.