강력한 패턴 매칭

패턴 매칭의 힘 발휘하기

`match` 표현식 기초

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

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

  match my_direction {
    Direction::North => println!("Going up!"),
    Direction::East => println!("Going right!"),
    Direction::South => println!("Going down!"),
    Direction::West => println!("Going left!"),
  }
}

리터럴과 범위 매칭하기

fn main() {
  let x = 7;

  match x {
    1 => println!("It's one!"),
    2 | 3 => println!("It's two or three!"),
    4..=8 => println!("It's between four and eight!"),
    _ => println!("It's something else!"), // Catch-all
  }

  let character = 'b';
  match character {
    'a'..='e' => println!("Early letter"),
    _ => println!("Other letter"),
  }
}

구조체 분해하기

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

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!("Not on an axis: ({}, {})", x, y),
  }
}

데이터가 있는 열거형 분해하기

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

fn process_message(msg: Message) {
  match msg {
    Message::Quit => println!("Quit message."),
    Message::Move { x, y } => {
      println!("Move to x: {}, y: {}", x, y);
    }
    Message::Write(text) => println!("Text message: {}", text),
    Message::ChangeColor(r, g, b) => {
      println!("Color: R:{}, G:{}, B:{}", r, g, b);
    }
  }
}

fn main() {
  process_message(Message::Move { x: 10, y: 20 });
  process_message(Message::Write(String::from("Hello!")));
}

와일드카드 패턴 `_`

fn main() {
  let some_value = Some(5);
  let absent_value: Option<i32> = None;

  match some_value {
    Some(x) => println!("Got a value: {}", x),
    _ => println!("Something else!"), // Matches None too
  }

  match absent_value {
    Some(x) => println!("Got a value: {}", x),
    _ => println!("No value here!"),
  }
}

단일 패턴에 사용하는 `if let`

fn main() {
  let config_max = Some(3u8);
  let none_value: Option<u8> = None;

  if let Some(max) = config_max {
    println!("Max configured to be: {}", max);
  }

  if let Some(val) = none_value {
    println!("This won't print: {}", val);
  } else {
    println!("No value found!");
  }
}

조건부 반복문에 사용하는 `while let`

fn main() {
  let mut stack = vec![1, 2, 3];

  while let Some(top) = stack.pop() {
    println!("Popped: {}", top);
  }

  println!("Stack is empty now.");
}

매치 가드: 조건 추가하기

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

  match num {
    Some(x) if x % 2 == 0 => println!("Even number: {}", x),
    Some(x) if x < 5 => println!("Small odd number: {}", x),
    Some(x) => println!("Any other number: {}", x),
    None => println!("No number"),
  }
}

패턴 매칭 도전 과제

enum Status {
  Loading,
  Success(u32),
  Error(String),
}

fn process_status(s: Status) {
  match s {
    Status::Success(code) if code > 200 => println!("Success with high code: {}", code),
    Status::Success(code) => println!("Success with code: {}", code),
    Status::Error(msg) => println!("Failed: {}", msg),
    _ => println!("Status unknown or loading..."),
  }
}

fn main() {
  process_status(Status::Success(201));
  process_status(Status::Error(String::from("Network issue")));
  process_status(Status::Loading);
  process_status(Status::Success(200));
}

복습: 패턴 완전히 익히기