Structs

Structs in rust let you structure data together. Similar to objects in javascript

struct User {
    active: bool,
    username: String,
    email: String,
    sign_in_count: u64,
}

fn main() {
    let user1 = User {
        active: true,
        username: String::from("someusername123"),
        email: String::from("someone@example.com"),
        sign_in_count: 1,
    };
    print!("User 1 username: {:?}", user1.username);
}

Can you guess if they are stored in stack or heap?

Side quest - Learning about traits

Try running experiments around

1. mutable and immutable references
2. Ownership transfer

for structs

Code 1 - Only stack types in the struct

struct User {
    active: bool,
    sign_in_count: u64,
}

fn main() {
    let mut user1 = User {
        active: true,
        sign_in_count: 1,
    };

    print_name(user1);
    print!("User 1 username: {}", user1.active); // Error - can not use borrowed value
}

fn print_name(user1: User) {
    print!("User 1 username: {}", user1.active);
}

Add the copy trait

#[derive(Copy, Clone)]
struct User {
    active: bool,
    sign_in_count: u64,
}

fn main() {
    let mut user1 = User {
        active: true,
        sign_in_count: 1,
    };

    print_name(user1);
    print!("User 1 username: {}", user1.active); // Error goes away because user1 is copied
}

fn print_name(user1: User) {
    print!("User 1 username: {}", user1.active);
}

Code 2 - Add strings

struct User {
    active: bool,
    sign_in_count: u64,
    username: String,
}

fn main() {
    let mut user1 = User {
        active: true,
        sign_in_count: 1,
        username: "harkirat".to_string()
    };

    change_name(user1);
    print!("User 1 username: {}", user1.active); // Error - can not use borrowed value
}

fn change_name(user1: User) {
    print!("User 1 username: {:?}", user1.active);
}

Try adding the Copy trait (you wont be able to because strings dont implement them, use clone trait instead)

#[derive(Clone)]
struct User {
    active: bool,
    sign_in_count: u64,
    username: String,
}

fn main() {
    let mut user1 = User {
        active: true,
        sign_in_count: 1,
        username: "harkirat".to_string()
    };

    change_name(user1.clone());
    print!("User 1 username: {}", user1.active); // Error - can not use borrowed value
}

fn change_name(user1: User) {
    print!("User 1 username: {:?}", user1.active);
}