Structs

A struct groups related data under one named type. It is the main way to model custom data in Rust.

Defining a struct

struct User {
    name: String,
    age: u32,
    active: bool,
}

Creating an instance

Fill every field by name. Access fields with a dot.

fn main() {
    let user = User {
        name: String::from("Alice"),
        age: 30,
        active: true,
    };
    println!("{} is {}", user.name, user.age);
}

To change fields, the instance must be declared with mut.

Methods with impl

An impl block adds methods to a struct. Methods take &self to borrow the instance.

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

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

    // Associated function (no self): acts like a constructor
    fn square(size: u32) -> Rectangle {
        Rectangle { width: size, height: size }
    }
}

fn main() {
    let rect = Rectangle { width: 4, height: 5 };
    println!("Area: {}", rect.area()); // 20

    let sq = Rectangle::square(3);
    println!("Area: {}", sq.area()); // 9
}

Associated functions are called with ::, while methods are called with ..