Methods

Methods are functions associated with a type. The self argument of a method is an instance of the type it is associated with:

struct Rectangle {
    width: u32,
    height: u32,
}

impl Rectangle {
    fn area(&self) -> u32 {
        self.width * self.height
    }

    fn inc_width(&mut self, delta: u32) {
        self.width += delta;
    }
}

fn main() {
    let mut rect = Rectangle { width: 10, height: 5 };
    println!("old area: {}", rect.area());
    rect.inc_width(5);
    println!("new area: {}", rect.area());
}

We will look much more at methods in today’s exercise and in tomorrow’s class.

Add a static method called Rectangle::new and call this from main:

fn new(width: u32, height: u32) -> Rectangle {
    Rectangle { width, height }
}

While technically, Rust does not have custom constructors, static methods are commonly used to initialize structs (but don’t have to). The actual constructor, Rectangle { width, height }, could be called directly. See the Rustnomicon.
Add a Rectangle::square(width: u32) constructor to illustrate that such static methods can take arbitrary parameters.

Comprehensive Rust 🦀

Methods