Enums

Rust allows you to define types called “enums” which enumerate possible values. Enums are a feature in many languages, but their capabilities differ in each language. Rust’s enums are most similar to algebraic data types in functional languages, such as F#, OCaml, and Haskell. Useful in combination with enums is Rust’s “pattern matching” facility, which makes it easy to run different code for different values of an enumeration.

Further information

Rustlings

enums1

 
// enums1.rs
// No hints this time! ;)

// I AM NOT DONE

#[derive(Debug)]
enum Message {
    // TODO: define a few types of messages as used below
}

fn main() {
    println!("{:?}", Message::Quit);
    println!("{:?}", Message::Echo);
    println!("{:?}", Message::Move);
    println!("{:?}", Message::ChangeColor);
}

enums2

 
// enums2.rs
// Execute `rustlings hint enums2` or use the `hint` watch subcommand for a hint.

// I AM NOT DONE

#[derive(Debug)]
enum Message {
    // TODO: define the different variants used below
}

impl Message {
    fn call(&self) {
        println!("{:?}", self);
    }
}

fn main() {
    let messages = [
        Message::Move { x: 10, y: 30 },
        Message::Echo(String::from("hello world")),
        Message::ChangeColor(200, 255, 255),
        Message::Quit,
    ];

    for message in &messages {
        message.call();
    }
}

enums3

 
// enums3.rs
// Address all the TODOs to make the tests pass!
// Execute `rustlings hint enums3` or use the `hint` watch subcommand for a hint.

// I AM NOT DONE

enum Message {
    // TODO: implement the message variant types based on their usage below
}

struct Point {
    x: u8,
    y: u8,
}

struct State {
    color: (u8, u8, u8),
    position: Point,
    quit: bool,
}

impl State {
    fn change_color(&mut self, color: (u8, u8, u8)) {
        self.color = color;
    }

    fn quit(&mut self) {
        self.quit = true;
    }

    fn echo(&self, s: String) {
        println!("{}", s);
    }

    fn move_position(&mut self, p: Point) {
        self.position = p;
    }

    fn process(&mut self, message: Message) {
        // TODO: create a match expression to process the different message variants
        // Remember: When passing a tuple as a function argument, you'll need extra parentheses: fn function((t, u, p, l, e))
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_match_message_call() {
        let mut state = State {
            quit: false,
            position: Point { x: 0, y: 0 },
            color: (0, 0, 0),
        };
        state.process(Message::ChangeColor(255, 0, 255));
        state.process(Message::Echo(String::from("hello world")));
        state.process(Message::Move(Point { x: 10, y: 15 }));
        state.process(Message::Quit);

        assert_eq!(state.color, (255, 0, 255));
        assert_eq!(state.position.x, 10);
        assert_eq!(state.position.y, 15);
        assert_eq!(state.quit, true);
    }
}