# 定义枚举
| enum IpAddrKind { |
| V4, |
| V6, |
| } |
最后一个 逗号 可加，可不加
# 枚举值
| let four = IpAddrKind::V4; |
| let six = IpAddrKind::V6; |
| |
| fn route(ip_type: IpAddrKind) { } |
| |
| struct IpAddr { |
| kind: IpAddrKind, |
| address: String |
| } |
# 枚举成员嵌套任意类型
| enum IpAddrKind { |
| V4(u8, u8, u8, u8), |
| V6(String), |
| } |
| |
| let home = IpAddrKind::V4(127, 0, 0, 1); |
| let loopback = IpAddrKind::V6("::1"); |
# 标准库如何定义 ip 地址？
| struct Ipv4Addr { |
| |
| } |
| |
| struct Ipv6Addr { |
| |
| } |
| |
| enum IpAddr { |
| V4(Ipv4Addr), |
| V6(Ipv6Addr), |
| } |
# 枚举还可以定义 impl
| enum Message { |
| Quit, |
| Move {x: i32, y: i32}, |
| Write(String), |
| ChangeColor(i32, i32, i32), |
| } |
| |
| |
| struct QuitMessage; |
| struct MoveMessage {x: i32, y: i32}; |
| struct WriteMessage(String); |
| struct ChangeColorMessage(i32, i32, i32); |
| |
| |
| impl Message { |
| fn call(&self) { |
| |
| } |
| } |
| |
| |
# Option
| enum Option<T> { |
| Some<T>, |
| None, |
| } |
因为常用，所以 Some 和 None 可单独使用。
例如：
| let some_number = Some(5); |
| |
| |
| let absent_number: Option<i32> = None; |
# match 控制流
| fn main() { |
| let coin = Coin::Penny; |
| let value = match coin { |
| Coin::Penny => { |
| println!("Penny"); |
| 1 |
| }, |
| Coin::Nickel => 5, |
| Coin::Dime => 10, |
| Coin::Quarter => 25, |
| }; |
| println!("{}", value); |
| } |
| |
| enum Coin { |
| Penny, |
| Nickel, |
| Dime, |
| Quarter |
| } |
# 绑定值的形式
| fn main() { |
| let coin = Coin::Quarter(UsState::Alaska); |
| let value = value_in_cents(coin); |
| println!("{}", value); |
| } |
| fn value_in_cents(coin: Coin) -> u8 { |
| match coin { |
| Coin::Penny => 1, |
| Coin::Nickel => 5, |
| Coin::Dime => 10, |
| Coin::Quarter(state) => { |
| println!("state: {:?}", state); |
| 25 |
| } |
| } |
| } |
| |
| #[derive(Debug)] |
| enum UsState { |
| Alabama, |
| Alaska, |
| |
| } |
| enum Coin { |
| Penny, |
| Nickel, |
| Dime, |
| Quarter(UsState) |
| } |
注意事项：
- 使用时，不要忘记前缀：
Coin:: - 使用时，不要忘记符号：
=> - 打印时，不要忘记注解和符号：
#derive(Debug) 和 {:?}
# 匹配 Option<T>
如何获取 Option 里面的值呢？
| fn plus_one(x: Option<i32>) -> Option<i32> { |
| match x { |
| None => None, |
| Some(i) => Some(i + 1) |
| } |
| } |
# 匹配是穷尽的
match 需要穷尽，如果某个分支没匹配到，就会编译不通过。
# _ 通配符
如果有些不想匹配，则可以用通配符，相当于 default 分支。
| let some_u8_value = 0u8; |
| match some_u8_value { |
| 1 => println!("one"), |
| 3 => println!("three"), |
| 5 => println!("five"), |
| 7 => println!("seven"), |
| _ => (), |
| } |
如果只考虑其中 1 个分支，就啰嗦了，因此有 if let
# if let 简化匹配
| let some_u8_value = Some(3); |
| |
| if let Some(3) = some_u8_value { |
| println!("three"); |
| } |
这样就不用每个分支都要穷尽。
