An Associated Function in Rust Does Not Need an Instance

A function inside an impl block that does not have a self parameter is an associated function rather than a method. We call it with Type::function(...). Constructors are often named new, but Rust does not treat that name specially in source.

struct Circle {
    radius: u32,
}
 
impl Circle {
    fn new(radius: u32) -> Self {
        Self { radius }
    }
}
 
fn main() {
    let circle = Circle::new(8);
    println!("Radius: {}", circle.radius);
}

Inside impl Circle, Self means Circle. There is no circle instance yet when we call Circle::new(8), so the function constructs and returns one.

This can feel like class methods in some other languages