Multiple Patterns and match guards

• https://rust-book.cs.brown.edu/ch18-03-pattern-syntax.html#multiple-patterns
• https://rust-book.cs.brown.edu/ch18-03-pattern-syntax.html#extra-conditionals-with-match-guards

Multiple patterns with |

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

with ..= syntax

let x = 5;

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

tuple을 분해하는 건 이미 알고있지

let x = (10, 'A');

match x {
    (num, alpha) => println!("num: {}, alpha: {}", num, alpha),
    _ => println!("something else"),
}

하지만 struct를 분해할 수도 있다는 건 몰랐을걸?

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

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

    let Point { x: a, y: b } = p;
    assert_eq!(0, a);
    assert_eq!(7, b);
    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 guard를 사용하면 추가적인 조건을 걸 수가 있지롱

let num = Some(4);

match num {
    Some(x) if x % 2 == 0 => println!("The number {} is even", x),
    Some(x) => println!("The number {} is odd", x),
    None => (),
}

@ bindings 를 사용하면 match guard 안에서 변수를 할당할 수 있지렁

enum Message {
    Hello {id: i32},
}
let msg = Message::Hello{id: 5};
match msg {
    Message::Hello { id } if id >=3 && id <= 7 => 
        println!("Found an id in range: {}", id),
    Message::Hello { id } => println!("Found some other id: {}", id),
}

이렇게 쓰지말고 아래처럼 쓰면 좀 더 깔끔하쥬

enum Message {
    Hello {id: i32},
}
let msg = Message::Hello{id: 5};
match msg {
    Message::Hello {id: _id @ 3..=7} =>
        println!("Found an id in range: {}", _id),
    Message::Hello { id } => println!("Found some other id: {}", id),
}