patterns_matching.md

匹配模式

fn main() {
  let favorite_color: Option<&str> = None;
  let is_tuesday = false;
  let age: Result<u8, _> = "34".parse();

  if let Some(color) = favorite_color {
    println!("Using your favorite color: {}, as the background color", color);
  } else if is_tuesday {
    println!("Tuesday is green day!");
  } else if let Ok(age) = age {
    if age > 30 {
      println!("Using purple as the background color");
    } else {
      println!("Using orange as the background color");
    }
  } else {
    println!("Using blue as the background color");
  }
}

fn main() {
  let mut stack = Vec::new();

  stack.push(1);
  stack.push(2);
  stack.push(3);

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

模式的两种形式

• 可辩驳：对某些可能的值，无法进行匹配模式：
  例如： if let Some(x) = xxx;

• 无可辩驳：能匹配任何可能的值的模式：
  例如： let x = 5;

• 函数参数， let 语句， for 循环只接收无可辩驳的模式

• if let 和 while let 可以接收可辩驳和无可辩驳的模式

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

enum Message {
  Quit,
  Move { x: f64, y: f64 },
  Write(String),
  ChangeColor(i32, i32, i32),
}


fn main() {
  let x = 1;

  match x {
    1 | 2 => println!("111"),
    3 | 4 => println!("34"),
    5..10 => println!("555...1000"),
    _ => {}
  }

  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),
    _ => {}
  }

  let msg = Message::ChangeColor(0, 345, 577);

  match msg {
    Message::Quit => println!("The qui"),
    Message::Move { x, y } => println!("The move"),
    Message::Write(text) => println!("The text {}", text),
    _ => {}
  }
}