Structs

Structs are like objects, except that they have a predefined structure with a set of keys that are known at compile time and guaranteed to be defined.

Structs can also, like most types, have an impl block associated with them which creates instance functions that you can call on an instance of that struct.

struct User {
    username,
    active,
}

impl User {
    fn set_active(self, active) {
        self.active = active;
    }

    fn describe(self) {
        if self.active {
            println!("{} is active.", self.username);
        } else {
            println!("{} is inactive.", self.username);
        }
    }
}

let user = User { username: "setbac", active: false };

user.describe();
user.set_active(true);
user.describe();

$> cargo run -- run scripts/book/structs/user_database.rn
setbac is inactive
setbac is active

Structs can also be pattern matched, like most types.

But since the fields of a struct are known at compile time, the compiler can ensure that you're only using fields which are defined.

struct User {
    username,
    active,
}

impl User {
    fn describe(self) {
        match self {
            User { username: "setbac", .. } => {
                println!("Yep, it's setbac.");
            }
            User { username, .. } => {
                println!("Other user: {username}.");
            }
        }
    }
}

let user = User { username: "setbac", active: false };

user.describe();
user.username = "newt";
user.describe();

$> cargo run -- run scripts/book/structs/struct_matching.rn
Yep, it's setbac.
Other user: newt.