Pattern Matching

        
          #[derive(Debug)]
enum Coin {
    Penny,
    Nickel,
    Dime,
    Quarter,
}

fn value_in_cents(coin: Coin) -> u8 {
    match coin {
        Coin::Penny => 1,
        Coin::Nickel => 5,
        Coin::Dime => 10,
        Coin::Quarter => 25,
    }
}

// Patterns with values
#[derive(Debug)]
enum UsState {
    Alabama,
    Alaska,
}

enum Coin2 {
    Penny,
    Nickel,
    Dime,
    Quarter(UsState),
}

fn value_in_cents2(coin: Coin2) -> u8 {
    match coin {
        Coin2::Penny => 1,
        Coin2::Nickel => 5,
        Coin2::Dime => 10,
        Coin2::Quarter(state) => {
            println!("State quarter from {:?}!", state);
            25
        }
    }
}

// Matching Option<T>
fn plus_one(x: Option<i32>) -> Option<i32> {
    match x {
        None => None,
        Some(i) => Some(i + 1),
    }
}

// Matching with if let (concise)
fn print_coin(coin: Coin2) {
    if let Coin2::Quarter(state) = coin {
        println!("State quarter from {:?}!", state);
    } else {
        println!("Not a state quarter");
    }
}

// Matching ranges
fn categorize_number(n: i32) {
    match n {
        0 => println!("Zero"),
        1..=9 => println!("Single digit"),
        10..=99 => println!("Double digit"),
        100..=999 => println!("Triple digit"),
        _ => println!("Large number"),
    }
}

// Matching structs
struct Point {
    x: i32,
    y: i32,
}

fn match_point(point: Point) {
    match point {
        Point { x: 0, y: 0 } => println!("Origin"),
        Point { x: 0, y } => println!("On y-axis at {}", y),
        Point { x, y: 0 } => println!("On x-axis at {}", x),
        Point { x, y } => println!("Point ({}, {})", x, y),
    }
}

// Matching with guards
fn number_info(n: i32) {
    match n {
        n if n < 0 => println!("Negative"),
        n if n % 2 == 0 => println!("Even positive"),
        n if n % 2 == 1 => println!("Odd positive"),
        _ => unreachable!(),
    }
}

// Matching vectors
fn match_vector(vec: &Vec<i32>) {
    match vec.as_slice() {
        [] => println!("Empty vector"),
        [x] => println!("Vector with one element: {}", x),
        [x, y] => println!("Vector with two elements: {}, {}", x, y),
        [x, y, rest @ ..] => println!("Vector: {}, {}, and {} more", x, y, rest.len()),
        _ => println!("Large vector"),
    }
}

fn main() {
    let coin = Coin::Quarter;
    println!("Coin value: {} cents", value_in_cents(coin));

    let coin2 = Coin2::Quarter(UsState::Alaska);
    println!("Coin2 value: {} cents", value_in_cents2(coin2));

    let five = Some(5);
    let six = plus_one(five);
    let none = plus_one(None);

    println!("five: {:?}, six: {:?}, none: {:?}", five, six, none);

    print_coin(Coin2::Quarter(UsState::Alabama));
    print_coin(Coin2::Penny);

    categorize_number(42);
    categorize_number(0);
    categorize_number(1000);

    let point = Point { x: 10, y: 20 };
    match_point(point);

    number_info(-5);
    number_info(4);
    number_info(7);

    let empty_vec = vec![];
    let one_vec = vec![1];
    let two_vec = vec![1, 2];
    let many_vec = vec![1, 2, 3, 4, 5];

    match_vector(&empty_vec);
    match_vector(&one_vec);
    match_vector(&two_vec);
    match_vector(&many_vec);
}