trpl-zh-cn/listings/ch06-enums-and-pattern-matching/listing-06-09/src/main.rs

#[derive(Debug)] // so we can inspect the state in a minute
enum UsState {
    Alabama,
    Alaska,
    // --snip--
}

impl UsState {
    fn existed_in(&self, year: u16) -> bool {
        match self {
            UsState::Alabama => year >= 1819,
            UsState::Alaska => year >= 1959,
            // -- snip --
        }
    }
}

enum Coin {
    Penny,
    Nickel,
    Dime,
    Quarter(UsState),
}

// ANCHOR: describe
fn describe_state_quarter(coin: Coin) -> Option<String> {
    let Coin::Quarter(state) = coin else {
        return None;
    };

    if state.existed_in(1900) {
        Some(format!("{state:?} is pretty old, for America!"))
    } else {
        Some(format!("{state:?} is relatively new."))
    }
}
// ANCHOR_END: describe

fn main() {
    if let Some(desc) = describe_state_quarter(Coin::Quarter(UsState::Alaska)) {
        println!("{desc}");
    }
}