枚举与模式匹配

枚举

enum IpAddrKind {
    V4,
    V6,
}
let four = IpAddrKind::V4;
let six = IpAddrKind::V6;

复杂情况:

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

Option是内置枚举内, 表示None:

let some_number = Some(5);
let some_string = Some("a string");

let absent_number: Option<i32> = None;

Match

fn plus_one(x: Option<i32>) -> Option<i32> {
    match x {
        None => None,
        Some(i) => Some(i + 1),
    }
}
let five = Some(5);
let six = plus_one(five);

可以设置所有值:

let some_u8_value = 0u8;
match some_u8_value {
    1 => println!("one"),
    3 => println!("three"),
    5 => println!("five"),
    7 => println!("seven"),
    _ => (),
}

if let 语法

let some_u8_value = Some(0u8);
match some_u8_value {
    Some(3) => println!("three"),
    _ => (),
}

可以换成:

let some_u8_value = Some(0u8);
if let Some(3) = some_u8_value {
    println!("three");
}