# 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
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`.