Pattern Matching

match target {
    pattern1 => expression1,
    pattern2 => {
        statement1;
        statement2;
        expression2
    },
    _ => expression3
}

if let pattern = target {
    statement;
    expression
}

while let pattern = target {
    statement;
}

Enum Pattern Matching

enum Action {
    Say(String),
    MoveTo(i32, i32),
    ChangeColorRGB(u16, u16, u16),
}

fn main() {
    let actions = [
        Action::Say("Hello Rust".to_string()),
        Action::MoveTo(1,2),
        Action::ChangeColorRGB(255,255,0),
    ];

    for action in actions {
        match action {
            Action::Say(s) => {
                println!("{}", s);
            },
            Action::MoveTo(x, y) => {
                println!("point from (0, 0) move to ({}, {})", x, y);
            },
            Action::ChangeColorRGB(r, g, _) => {
                println!("change color into '(r:{}, g:{}, b:0)', 'b' has been ignored",
                    r, g,
                );
            }
        }
    }
}

Tuple Pattern Matching

fn main() {
    let numbers = (2, 4, 8, 16, 32);

    match numbers {
        (first, .., last) => {
            println!("Some numbers: {}, {}", first, last);
        },
    }
}

Struct Pattern Matching

struct Point {
    x: i32,
    y: i32,
    z: i32,
}

fn main() {
    let p = Point { x: 0, y: 7, z: 0 };
    let Point { x: a, y: b, z: c } = p;
    assert_eq!(0, a);
    assert_eq!(7, b);
    assert_eq!(0, c);

    let origin = Point { x: 0, y: 0, z: 0 };
    match origin {
        Point { x, .. } => println!("x is {}", x),
    }
}

fn main() {
    let p = Point { x: 0, y: 7 };

    match p {
        Point { x, y: 0 } => println!("On the x axis at {}", x),
        Point { x: 0, y } => println!("On the y axis at {}", y),
        Point { x, y } => println!("On neither axis: ({}, {})", x, y),
    }
}

Match Guard

Combine pattern matching and if expression:

let num = Some(4);

match num {
    Some(x) if x < 5 => println!("less than five: {}", x),
    Some(x) => println!("{}", x),
    None => (),
}

Match Assignment

Combine pattern matching and @ expression:

enum Message {
    Hello { id: i32 },
}

let msg = Message::Hello { id: 5 };

match msg {
    Message::Hello { id: id_variable @ 3..=7 } => {
        println!("Found an id in range: {}", id_variable)
    },
    Message::Hello { id: 10..=12 } => {
        println!("Found an id in another range")
    },
    Message::Hello { id } => {
        println!("Found some other id: {}", id)
    },
}

struct Point {
    x: i32,
    y: i32,
}

fn main() {
    let p @ Point {x: px, y: py } = Point {x: 10, y: 23};
    println!("x: {}, y: {}", px, py);
    println!("{:?}", p);

    let point = Point {x: 10, y: 5};
    if let p @ Point {x: 10, y} = point {
        println!("x is 10 and y is {} in {:?}", y, p);
    } else {
        println!("x was not 10 :(");
    }
}