src/doc/rust-by-example/src/traits/disambiguating.md

   1 # Disambiguating overlapping traits
   2
   3 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!
   4
   5 Good news: because each trait implementation gets its own `impl` block, it's
   6 clear which trait's `get` method you're implementing.
   7
   8 What about when it comes time to _call_ those methods? To disambiguate between
   9 them, we have to use Fully Qualified Syntax.
  10
  11 ```rust,editable
  12 trait UsernameWidget {
  13     // Get the selected username out of this widget
  14     fn get(&self) -> String;
  15 }
  16
  17 trait AgeWidget {
  18     // Get the selected age out of this widget
  19     fn get(&self) -> u8;
  20 }
  21
  22 // A form with both a UsernameWidget and an AgeWidget
  23 struct Form {
  24     username: String,
  25     age: u8,
  26 }
  27
  28 impl UsernameWidget for Form {
  29     fn get(&self) -> String {
  30         self.username.clone()
  31     }
  32 }
  33
  34 impl AgeWidget for Form {
  35     fn get(&self) -> u8 {
  36         self.age
  37     }
  38 }
  39
  40 fn main() {
  41     let form = Form{
  42         username: "rustacean".to_owned(),
  43         age: 28,
  44     };
  45
  46     // If you uncomment this line, you'll get an error saying
  47     // "multiple `get` found". Because, after all, there are multiple methods
  48     // named `get`.
  49     // println!("{}", form.get());
  50
  51     let username = <Form as UsernameWidget>::get(&form);
  52     assert_eq!("rustacean".to_owned(), username);
  53     let age = <Form as AgeWidget>::get(&form);
  54     assert_eq!(28, age);
  55 }
  56 ```
  57
  58 ### See also:
  59
  60 [The Rust Programming Language chapter on Fully Qualified syntax][trpl_fqsyntax]
  61
  62 [trpl_fqsyntax]: https://doc.rust-lang.org/book/ch19-03-advanced-traits.html#fully-qualified-syntax-for-disambiguation-calling-methods-with-the-same-name