New upstream version 1.63.0+dfsg1

[rustc.git] / src / doc / rust-by-example / src / trait / disambiguating.md

# 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.

```rust,editable
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);
}
```

### See also:

[The Rust Programming Language chapter on Fully Qualified syntax][trpl_fqsyntax]

[trpl_fqsyntax]: https://doc.rust-lang.org/book/ch19-03-advanced-traits.html#fully-qualified-syntax-for-disambiguation-calling-methods-with-the-same-name