Disambiguating overlapping traits
A type can implement many different traits. What if two traits both require
the same name for a function? 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); }
See also:
The Rust Programming Language chapter on Fully Qualified syntax