Trait Objects

Exercises

Returning and passing to functions

// Make the code compile by completing the function signatures.

trait Shape {
    fn shape(&self) -> String;
}

struct Triangle;

struct Square;

impl Shape for Triangle {
    fn shape(&self) -> String {
        "🔺".to_string()
    }
}

impl Shape for Square {
    fn shape(&self) -> String {
        "🟥".to_string()
    }
}

fn get_shape(side_count: u8) ->  {
    match side_count {
        3 => Box::new(Triangle),
        4 => Box::new(Square),
        _ => panic!("No shape with side count available"),
    }
}

fn draw_shape(to_draw: &) {
    println!("{}", to_draw.shape())
}

fn main() {
    let my_shape = get_shape(4);
    draw_shape(my_shape.as_ref());
}

trait Shape {
  fn shape(&self) -> String;
}

struct Triangle;

struct Square;

impl Shape for Triangle {
  fn shape(&self) -> String {
      "🔺".to_string()
  }
}

impl Shape for Square {
  fn shape(&self) -> String {
      "🟥".to_string()
  }
}

fn get_shape(side_count: u8) -> Box<dyn Shape> {
  match side_count {
      3 => Box::new(Triangle),
      4 => Box::new(Square),
      _ => panic!("No shape with side count available"),
  }
}

fn draw_shape(to_draw: &dyn Shape) {
  println!("{}", to_draw.shape())
}

fn main() {
  let my_shape = get_shape(4);
  draw_shape(my_shape.as_ref());
}

Trait objects vectors

// Make the code compile by annotating the type for the vector.

trait Shape {
    fn shape(&self) -> String;
    fn side_count(&self) -> u8;
}

struct Triangle;

struct Square;

impl Shape for Triangle {
    fn shape(&self) -> String {
        "🔺".to_string()
    }
    fn side_count(&self) -> u8 {
        3
    }
}

impl Shape for Square {
    fn shape(&self) -> String {
        "🟥".to_string()
    }
    fn side_count(&self) -> u8 {
        4
    }
}

fn main() {
    let shape1 = Square;
    let shape2 = Square;
    let shape3 = Triangle;
    let shapes = vec![&shape1, &shape2, &shape3];

    // fetch the first triangle and print it
    for shape in shapes {
        if shape.side_count() == 3 {
            println!("{}", shape.shape());
            break;
        }
    }
}

trait Shape {
  fn shape(&self) -> String;
  fn side_count(&self) -> u8;
}

struct Triangle;

struct Square;

impl Shape for Triangle {
  fn shape(&self) -> String {
      "🔺".to_string()
  }
  fn side_count(&self) -> u8 {
      3
  }
}

impl Shape for Square {
  fn shape(&self) -> String {
      "🟥".to_string()
  }
  fn side_count(&self) -> u8 {
      4
  }
}

fn main() {
  let shape1 = Square;
  let shape2 = Square;
  let shape3 = Triangle;
  let shapes: Vec<&dyn Shape> = vec![&shape1, &shape2, &shape3];

  // fetch the first triangle and print it
  for shape in shapes {
      if shape.side_count() == 3 {
          println!("{}", shape.shape());
          break;
      }
  }
}