trait noisy { fn speak(); } struct cat : noisy { priv { mut meows : uint, fn meow() { error!("Meow"); self.meows += 1u; if self.meows % 5u == 0u { self.how_hungry += 1; } } } mut how_hungry : int, name : ~str, fn speak() { self.meow(); } fn eat() -> bool { if self.how_hungry > 0 { error!("OM NOM NOM"); self.how_hungry -= 2; return true; } else { error!("Not hungry!"); return false; } } } fn cat(in_x : uint, in_y : int, in_name: ~str) -> cat { cat { meows: in_x, how_hungry: in_y, name: in_name } } fn main() { let nyan : noisy = cat(0u, 2, ~"nyan") as noisy; nyan.speak(); }