polymorphism.rs

trait Fruit {
  fn eat(&self);
}

struct Apple {
  x: int
}

impl Fruit for Apple {
  fn eat(&self) {
    println(fmt!("Crunching on apple (%d)", self.x));
  }
}

struct Banana {
  y: int
}

impl Fruit for Banana {
  fn eat(&self) {
    println(fmt!("Munching on banana (%d)", self.y));
  }
}

fn main() {
  let managed: ~[ @Fruit ] = ~[
    @Apple{ x: 1 } as @Fruit,
    @Banana{ y: 2 } as @Fruit
  ];
  let owned: ~[ ~Fruit ] = ~[
    ~Apple{ x: 1 } as ~Fruit,
    ~Banana{ y: 2 } as ~Fruit
  ];

  println(~"This eats both fruit, as expected:");
  for managed.each |fruit| {
    fruit.eat();
  }

  println(~"This only eats the apple - why?!");
  for owned.each |fruit| {
    fruit.eat();
  }
}