# 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> {
        // The 'a defines a lifetime
        name: &'a str,
        age: u8,
    }

    // A unit struct
    struct Unit;

    // 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 {
        // A rectangle can be specified by where the top left and bottom right
        // corners are in space.
        top_left: Point,
        bottom_right: 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: 10.3, 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 bottom_right = Point { x: 5.2, ..point };

        // `bottom_right.y` will be the same as `point.y` because we used that field
        // from `point`
        println!("second point: ({}, {})", bottom_right.x, bottom_right.y);

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

        let _rectangle = Rectangle {
            // struct instantiation is an expression too
            top_left: Point { x: left_edge, y: top_edge },
            bottom_right: bottom_right,
        };

        // Instantiate a unit struct
        let _unit = Unit;

        // 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`, lifetime and destructuring