Methods

  struct Point {
      x: f64,
      y: f64,
  }

  // Implementation block, all `Point` methods go in here
  impl Point {
      // This is a static method
      // Static methods don't need to be called by an instance
      // These methods are generally used as constructors
      fn origin() -> Point {
          Point { x: 0.0, y: 0.0 }
      }

      // Another static method, taking two arguments:
      fn new(x: f64, y: f64) -> Point {
          Point { x: x, y: y }
      }
  }

  struct Rectangle {
      p1: Point,
      p2: Point,
  }

  impl Rectangle {
      // This is an instance method
      // `&self` is sugar for `self: &Self`, where `Self` is the type of the
      // caller object. In this case `Self` = `Rectangle`
      fn area(&self) -> f64 {
          // `self` gives access to the struct fields via the dot operator
          let Point { x: x1, y: y1 } = self.p1;
          let Point { x: x2, y: y2 } = self.p2;

          // `abs` is a `f64` method that returns the absolute value of the
          // caller
          ((x1 - x2) * (y1 - y2)).abs()
      }

      fn perimeter(&self) -> f64 {
          let Point { x: x1, y: y1 } = self.p1;
          let Point { x: x2, y: y2 } = self.p2;

          2.0 * ((x1 - x2).abs() + (y1 - y2).abs())
      }

      // This method requires the caller object to be mutable
      // `&mut self` desugars to `self: &mut Self`
      fn translate(&mut self, x: f64, y: f64) {
          self.p1.x += x;
          self.p2.x += x;

          self.p1.y += y;
          self.p2.y += y;
      }
  }

  // `Pair` owns resources: two heap allocated integers
  struct Pair(Box<i32>, Box<i32>);

  impl Pair {
      // This method "consumes" the resources of the caller object
      // `self` desugars to `self: Self`
      fn destroy(self) {
          // Destructure `self`
          let Pair(first, second) = self;

          println!("Destroying Pair({}, {})", first, second);

          // `first` and `second` go out of scope and get freed
      }
  }

  fn main() {
      let rectangle = Rectangle {
          // Static methods are called using double colons
          p1: Point::origin(),
          p2: Point::new(3.0, 4.0),
      };

      // Instance methods are called using the dot operator
      // Note that the first argument `&self` is implicitly passed, i.e.
      // `rectangle.perimeter()` === `Rectangle::perimeter(&rectangle)`
      println!("Rectangle perimeter: {}", rectangle.perimeter());
      println!("Rectangle area: {}", rectangle.area());

      let mut square = Rectangle {
          p1: Point::origin(),
          p2: Point::new(1.0, 1.0),
      };

      // Error! `rectangle` is immutable, but this method requires a mutable
      // object
      //rectangle.translate(1.0, 0.0);
      // TODO ^ Try uncommenting this line

      // Okay! Mutable objects can call mutable methods
      square.translate(1.0, 1.0);

      let pair = Pair(Box::new(1), Box::new(2));

      pair.destroy();

      // Error! Previous `destroy` call "consumed" `pair`
      //pair.destroy();
      // TODO ^ Try uncommenting this line
  }
Rectangle perimeter: 14
Rectangle area: 12
Destroying Pair(1, 2)