# 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.

    #[derive(Debug)]
    struct Person<'a> {
        name: &'a str,
        age: u8,
    }

    // A unit struct
    struct Nil;

    // A tuple struct
    struct Pair(i32, f32);

    // A struct with two fields
    struct Point {
        x: f32,
        y: f32,
    }

    // Structs can be reused as fields of another struct
    #[allow(dead_code)]
    struct Rectangle {
        p1: Point,
        p2: Point,
    }

    fn main() {
        // Create struct with field init shorthand
        let name = "Peter";
        let age = 27;
        let peter = Person { name, age };

        // Print debug struct
        println!("{:?}", peter);

        // Instantiate a `Point`
        let point: Point = Point { x: 0.3, y: 0.4 };

        // Access the fields of the point
        println!("point coordinates: ({}, {})", point.x, point.y);

        // Make a new point by using struct update syntax to use the fields of our other one
        let new_point = Point { x: 0.1, ..point };
        // `new_point.y` will be the same as `point.y` because we used that field from `point`
        println!("second point: ({}, {})", new_point.x, new_point.y);

        // Destructure the point using a `let` binding
        let Point { x: my_x, y: my_y } = point;

        let _rectangle = Rectangle {
            // struct instantiation is an expression too
            p1: Point { x: my_y, y: my_x },
            p2: point,
        };

        // Instantiate a unit struct
        let _nil = Nil;

        // Instantiate a tuple struct
        let pair = Pair(1, 0.1);

        // Access the fields of a tuple struct
        println!("pair contains {:?} and {:?}", pair.0, pair.1);

        // Destructure a tuple struct
        let Pair(integer, decimal) = pair;

        println!("pair contains {:?} and {:?}", integer, decimal);
    }

### 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