5.1 Defining and Instantiating Structs

Struct

• Like Tuple, hold multiple related values.
• Unlike Tuple, each data has its name.
• To get a specific value from a struct, we use dot notation.

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

• Use string because reference cannot be stored without specifying lifetimes.

Instantiating Structs

Using Default Initializer

fn main() {
    let user1 = User {
        active: true,
        username: String::from("someusername123"),
        email: String::from("[email protected]"),
        sign_in_count: 1,
    };
		//mutable version
    let mut user2 = User {
        active: true,
        username: String::from("someusername123"),
        email: String::from("[email protected]"),
        sign_in_count: 1,
    };

    user2.email = String::from("[email protected]");

}

• Entire instance can be mutable.
• Rust doesn’t allow us to mark only certain fields as mutable.

Using Function

fn build_user(email: String, username: String) -> User {
    User {
        active: true,
        username: username,
        email: email,
        sign_in_count: 1,
    }
}

fn main() {
    let user1 = build_user(
        String::from("[email protected]"),
        String::from("someusername123"),
    );
}

Using Field Init Shorthand

fn build_user(email: String, username: String) -> User {
    User {
        active: true,
        username,
        email,
        sign_in_count: 1,
    }
}

fn main() {
    let user1 = build_user(
        String::from("[email protected]"),
        String::from("someusername123"),
    );
}