走进 Rust:枚举
Rust About 1,495 words定义枚举
#[derive(Debug)]
enum IpAddrKind {
V4,
V6,
}
使用枚举
枚举同样可以使用impl
来实现结构体中的方法功能。
fn main() {
let m = Message::Write(String::from("hello"));
m.call();
}
enum Message {
Quit,
Move { x: i32, y: i32 },
Write(String),
ChangeColor(i32, i32, i32),
}
impl Message {
fn call(&self) {
// method body would be defined here
}
}
模式匹配
必须全匹配,若缺少一项,比如None
,编译将无法通过。
#[derive(Debug)]
enum UsState {
Alabama,
Alaska,
}
enum Coin {
Penny,
Nickel,
Dime,
Quarter(UsState),
}
fn value_in_cents(coin: Coin) -> u8 {
match coin {
Coin::Penny => 1,
Coin::Nickel => 5,
Coin::Dime => 10,
Coin::Quarter(state) => {
println!("State quarter from {:?}!", state);
25
},
}
}
fn main() {
value_in_cents(Coin::Quarter(UsState::Alabama));
}
搭配 Option
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);
_占位符
可以使用_
来代替默认行为,否则将无线穷举。
let some_u8_value = 0u8;
match some_u8_value {
1 => println!("one"),
3 => println!("three"),
5 => println!("five"),
7 => println!("seven"),
_ => (),
}
if let
使用if let
可以简化匹配。
let mut count = 0;
if let Coin::Quarter(state) = Coin::Quarter(UsState::Alaska) {
println!("State quarter from {:?}!", state);
} else {
count += 1;
}
Views: 2,643 · Posted: 2020-07-13
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