rust-book/pattern_matching/src/main.rs

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

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

enum Color {
    Rgb(i32, i32, i32),
    Hsv(i32, i32, i32)
}

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

fn match_variable_shadowing () {
    let x = Some(5);
    let y = 10;

    match x {
        Some(50) => println!("Got 50"),

        // shadows the outer y, gets the value of x
        Some(y) => println!("Matched, y = {:?}", y),

        _ => println!("Default case, x = {:?}", x),
    }

    println!("at the end: x = {:?}, y = {:?}", x, y);
}

fn match_multiple () {
    let x = 1;

    match x {
        1 | 2 => println!("one or two"),
        3 => println!("three"),
        _ => println!("anything"),
    }
}

fn match_range () {
    let x = 5;

    match x {
        1 ... 5 => println!("one through five"),
        _ => println!("something else"),
    }
}

fn match_destructure_with_literals () {
    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),
    }
}

fn match_destructure_enum () {
    let msg = Message::ChangeColor(Color::Hsv(0, 160, 255));

    match msg {
        Message::ChangeColor(Color::Rgb(r, g, b)) => {
            println!(
                "Change the color to red {}, green {}, and blue {}",
                r,
                g,
                b
            )
        },
        Message::ChangeColor(Color::Hsv(h, s, v)) => {
            println!(
                "Change the color to hue {}, saturation {}, and value {}",
                h,
                s,
                v
            )
        }
        _ => ()
    }
}

fn destructure_references() {
    let points = vec![
        Point { x: 0, y: 0 },
        Point { x: 1, y: 5 },
        Point { x: 10, y: -3 },
    ];

    let sum_of_squares: i32 = points
        .iter()
        .map(|&Point { x, y }| x * x + y * y)
        .sum();
}

fn match_ignore_value () {
    let mut setting_value = Some(5);
    let new_setting_value = Some(10);

    match (setting_value, new_setting_value) {
        (Some(_), Some(_)) => {
            println!("Can't overwrite an existing customized value");
        }
        _ => {
            setting_value = new_setting_value;
        }
    }

    println!("setting is {:?}", setting_value);
}

fn match_ignore_value_parts () {
    let origin = XYZPoint { x: 0, y: 0, z: 0 };

    match origin {
        XYZPoint { x, .. } => println!("x is {}", x),
    }
}

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

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

fn match_guard() {
    let num = Some(4);

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

fn match_variable_shadowing_fixed_with_match_guard() {
    let x = Some(5);
    let y = 10;

    match x {
        Some(50) => println!("Got 50"),
        Some(n) if n == y => println!("Matched, n = {:?}", n),
        _ => println!("Default case, x = {:?}", x),
    }

    println!("at the end: x = {:?}, y = {:?}", x, y);
}

fn at_match_var_bind() {
    enum Message {
        Hello { id: i32 },
    }

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

    match msg {
        Message::Hello { id: id_variable @ 3...7 } => { // The @ binds the value and matches
            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)
        },
    }
}

fn main() {
    match_variable_shadowing();
    match_multiple();
    match_range();
    match_destructure_with_literals();
    match_destructure_enum();
    destructure_references();
    match_ignore_value();
    match_ignore_value_parts();
    match_ignore_value_parts_tuple();
    match_guard();
    match_variable_shadowing_fixed_with_match_guard();
    at_match_var_bind();
}