Rust methods are like functions defined in the context of a struct

(or an enum or a trait object). The first parameter to the function is always self, which represents the instance of the struct that the method is called on. Here’s an example

#[derive(Debug)]
struct Rectangle {
    width: u32,
    height: u32,
}


impl Rectangle {
    // here's the method
    fn area(&self) -> u32 {
        //  ^^^^^ this is an alias for self: &Self
        self.width * self.height
    }
    // there could be more things associated with Rectangle here inside this impl block
}

fn main() {
    let rect1 = Rectangle {
        width: 30,
        height: 50,
    };

    println!(
        "The area of the rectangle is {} square pixels.",
        rect1.area()  // call the method with dot notation on the struct instance
    );
}

Note that methods can take ownership of self (though this is pretty rare), borrow self immutably as we’ve done here, or borrow self mutably, just as they can any other parameter.

Sources

• The Rust Book chapter 5.3