User Interfaces

Declaration

An interface declares a behavior shared by many types. Any struct or enum can promise it:

interface Pet {
  pub fn name(*const self) String;
}

Implement

Types opt in with implement blocks and write the promised methods inside. There are no inherent impl blocks: free functions and methods live in struct bodies, interfaces only describe them.

use std.string;

struct Cat {
  pub nickname: String,
}

implement Pet : Cat {
  fn name(*const self) String {
    String.from("cat")
  }
}

Bounds

Interfaces bound generics. A function over T: Pet accepts any type with that behavior and nothing else:

fn greet[T: Pet](pet: T) {
  @println("hi {}", pet.name());
}

greet(Cat { .nickname = String.from("tom") });

implement blocks can be generic and bounded too: Box[T] is Copy exactly when T is.

implement[T: Copy] Copy : Box[T] {}