enums

Enums and Pattern Matching

Enums

We can create enums via the enum keyword. We can even assign data to each case.

enum Message {
    Quit,  // No data associated
    Move {x: i32, y: i32},  // Anonymous struct
    Write(String),  // Includes a single String
    ChangeColor(i32, i32, i32),  // Includes three i32 values
}

Similarly to structs, we can also use impl to define methods on enums.

The Option<T> enum allows us to express missing values without having the null concept.

enum Option<T> {
    Some(T),
    None,
}

Pattern matching

We can use match and the compiler will check if we're exhaustive for enums. The _ pattern will match any value.

If we only care about one particular case, and maybe a _, like

let some_u8_value = Some(0u8);
match some_u8_value {
    Some(3) => println!("three"),
    _ => println!("not three"),
}

Then we can use the if let shorthand:

if let Some(3) = some_u8_value {
    println!("three");
} else {
    println!("not three");
}

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