rust-day1-枚举

rust-枚举和模式匹配「rustwiki.org」

看看代码，熟悉语法，概念和其他语言基本一致。

枚举定义

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

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

struct QuitMessage; // 类单元结构体
struct MoveMessage {
    x: i32,
    y: i32,
}
struct WriteMessage(String); // 元组结构体
struct ChangeColorMessage(i32, i32, i32); // 元组结构体


impl Message {
    fn call(&self) {
        // 在这里定义方法体
    }
}

match匹配

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
enum Coin {
    Penny,
    Nickel,
    Dime,
    Quarter,
}

fn value_in_cents(coin: Coin) -> u8 {
    match coin {
        Coin::Penny => 1,
        Coin::Nickel => 5,
        Coin::Dime => 10,
        Coin::Quarter => 25,
    }
}

fn main() {}

Option

1
2
3
4
enum Option<T> {
    Some(T),
    None,
}

match Option

1
2
3
4
5
6
7
8
9
10
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);
let none = plus_one(None);

if let 简化match

类似java streamapi中 ifPresent

1
2
3
if let Some(3) = some_u8_value {
    println!("three");
}

加上else

1
2
3
4
5
6
let mut count = 0;
if let Coin::Quarter(state) = coin {
    println!("State quarter from {:?}!", state);
} else {
    count += 1;
}