Idiomatic Rust Snippets

What is an enum?

Enums in Rust are a way to define a type by enumerating its possible values. They are similar to enums in other programming languages but are more powerful because each variant of an enum can have associated data. Enums are used to represent a value that could be one of several different types.

Defining Enums

Enums are defined using the enum keyword, followed by the name of the enum and its variants.

Here is an example of a basic enum:

enum Direction {
    North,
    South,
    East,
    West,
}

fn main() {
    let direction = Direction::North;

    match direction {
        Direction::North => println!("Heading North!"),
        Direction::South => println!("Heading South!"),
        Direction::East => println!("Heading East!"),
        Direction::West => println!("Heading West!"),
    }
}

Enums can have variants with associated data, which makes them very powerful. Here is an example:

enum Message {
    Quit,
    Move { x: i32, y: i32 },
    Write(String),
    ChangeColor(i32, i32, i32),
}

fn main() {
    let msg1 = Message::Quit;
    let msg2 = Message::Move { x: 10, y: 20 };
    let msg3 = Message::Write(String::from("Hello"));
    let msg4 = Message::ChangeColor(255, 0, 0);

    match msg1 {
        Message::Quit => println!("Quit message"),
        Message::Move { x, y } => println!("Move to ({}, {})", x, y),
        Message::Write(text) => println!("Write message: {}", text),
        Message::ChangeColor(r, g, b) => println!("Change color to ({}, {}, {})", r, g, b),
    }
}

You can also define methods on enums using the impl keyword. Here is an example:

enum Message {
    Quit,
    Move { x: i32, y: i32 },
    Write(String),
    ChangeColor(i32, i32, i32),
}

impl Message {
    fn call(&self) {
        match self {
            Message::Quit => println!("Quit message"),
            Message::Move { x, y } => println!("Move to ({}, {})", x, y),
            Message::Write(text) => println!("Write message: {}", text),
            Message::ChangeColor(r, g, b) => println!("Change color to ({}, {}, {})", r, g, b),
        }
    }
}

fn main() {
    let msg = Message::Write(String::from("Hello"));
    msg.call();
}