枚举与模式匹配

枚举

定义枚举

枚举值

将数据附加到枚举的变体中

标准库中的IpAddr

案例

Option枚举

Rust没有Null

Rust中类似null的概念

Option 比Null好在哪里?

控制流运算符match

强大的控制流运算符match

案例

#[derive(Debug)]
enum UsState{
    Alabama,
    Alaska,
}
enum Coin {
    Penny,
    Nickel,
    Dime,
    Quarter(UsState)
}
fn value_in_us_cents(coin:Coin)-> u8{
    match coin{
        Coin::Penny=>{
            println!("Penny");
            1
        }
        Coin::Nickel=>5,
        Coin::Dime=>10,
        Coin::Quarter(state)=>{
            println!("State quarter from {:?}!",state);
            25
        }
    }
}
fn main() {
    let c =Coin::Quarter(UsState::Alabama);
    println!("{}",value_in_us_cents(c));
    println!("Hello, world!");
}

匹配Option

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

if let

fn main() {
    let v =Some(0u8);
    match v {
        Some(3)=>println!("3"),
        // Some(4)=>println!("4"),
        // Some(5)=>println!("5"),
        // Some(6)=>println!("6"),
        _=>(),
    }
    if let Some(3) = v {println!("3");}
}

fn main() {
    let v =Some(0u8);
    match v {
        Some(3)=>println!("3"),
        // Some(4)=>println!("4"),
        // Some(5)=>println!("5"),
        // Some(6)=>println!("6"),
        _=>(),
    }
    if let Some(3) = v {
        println!("3");
    }else{
        println!("other");
    }
}