Rust中支持模式匹配的位置:

1. let声明
2. 函数和闭包参数
3. match表达式
4. if let表达式
5. while let 表达式
6. for 表达式

let 声明

fn main() {
    let (a, b) = (1, 2);
    let Point { x, y } = Point { x: 1, y: 2 };
    assert_eq!(1, a);
    assert_eq!(2, b);
    assert_eq!(1, x);
    assert_eq!(2, y);
}
struct Point {
    x: i32,
    y: i32,
}

函数和闭包的参数位置 ref 模式

fn main() {
    let s = sum("1".to_string(), "2".to_string());
    assert_eq!(s, "12".to_string());
}
fn sum(x: String, ref y: String) -> String {
    x + y
}

ref 就是引用模式 借用的意思

fn main() {
    let a = 42;
    let ref b = a;
    let c = &a;
    assert_eq!(b, c);
    let mut a = [1, 2, 3];
    let ref mut b = a;
    b[0] = 0;
    assert_eq!(a, [0, 2, 3]);
}

match表达式

fn check_optional(opt: Option<i32>) {
    match opt {
        Some(p) => println!("has value {}", p),
        None => println!("has no value"),
    }
}
fn handle_result(res: i32) -> Result<i32, dyn Error> {
    do_someting(res)?;
    //？等价于下面
    match do_someting(res) {
        ok(0) => Ok(o),
        Err(e) => SomeError(e),
    }
}

if let

fn main() {
    let x = &Some(3);
    if let Some(y) = x { //进行相互转换
        println!("1");
        y;
    }
}