Structures

There are three types of structures (“structs”) that can be created using the
struct keyword:

  • Tuple structs, which are, basically, named tuples.
  • The classic C structs
  • Unit structs, which are field-less, are useful for generics.
  1. #[derive(Debug)]
  2. struct Person<'a> {
  3.     name: &'a str,
  4.     age: u8,
  5. }
  7. // A unit struct
  8. struct Nil;
  10. // A tuple struct
  11. struct Pair(i32, f32);
  13. // A struct with two fields
  14. struct Point {
  15.     x: f32,
  16.     y: f32,
  17. }
  19. // Structs can be reused as fields of another struct
  20. #[allow(dead_code)]
  21. struct Rectangle {
  22.     p1: Point,
  23.     p2: Point,
  24. }
  26. fn main() {
  27.     // Create struct with field init shorthand
  28.     let name = "Peter";
  29.     let age = 27;
  30.     let peter = Person { name, age };
  32.     // Print debug struct
  33.     println!("{:?}", peter);
  36.     // Instantiate a `Point`
  37.     let point: Point = Point { x: 0.3, y: 0.4 };
  39.     // Access the fields of the point
  40.     println!("point coordinates: ({}, {})", point.x, point.y);
  42.     // Make a new point by using struct update syntax to use the fields of our other one
  43.     let new_point = Point { x: 0.1, ..point };
  44.     // `new_point.y` will be the same as `point.y` because we used that field from `point`
  45.     println!("second point: ({}, {})", new_point.x, new_point.y);
  47.     // Destructure the point using a `let` binding
  48.     let Point { x: my_x, y: my_y } = point;
  50.     let _rectangle = Rectangle {
  51.         // struct instantiation is an expression too
  52.         p1: Point { x: my_y, y: my_x },
  53.         p2: point,
  54.     };
  56.     // Instantiate a unit struct
  57.     let _nil = Nil;
  59.     // Instantiate a tuple struct
  60.     let pair = Pair(1, 0.1);
  62.     // Access the fields of a tuple struct
  63.     println!("pair contains {:?} and {:?}", pair.0, pair.1);
  65.     // Destructure a tuple struct
  66.     let Pair(integer, decimal) = pair;
  68.     println!("pair contains {:?} and {:?}", integer, decimal);
  69. }

Activity

  1. Add a function rect_area which calculates the area of a rectangle (try
    using nested destructuring).
  2. Add a function square which takes a Point and a f32 as arguments, and returns a Rectangle with its lower left corner on the point, and a width and height corresponding to the f32.

See also:

attributes and destructuring