traits.rs

struct PositionData {
    x: int,
    y: int
}

trait Position {
  fn position(&self) -> PositionData;
}

trait Color {
  fn color(&self) -> int;
}

trait Renderable : Position + Color {}

struct Light {
  position: PositionData,
  color: int
}

impl Position for Light {
  fn position(&self) -> PositionData { self.position } 
}

impl Color for Light {
  fn color(&self) -> int { self.color } 
}

impl Renderable for Light {}

would_like_to_write.rs

struct PositionData {
    x: int,
    y: int
}

trait Position {
  position: PositionData;
}

trait Color {
  color: int;
}

trait Renderable : Position + Color {}

struct Light {
  position: PositionData,
  color: int
}

impl Renderable for Light {}