Rust for C-Programmers

10.8 Enums in Collections and Functions

Even if the variants store different amounts of data, the compiler treats the enum as a single type.

10.8.1 Storing Enums in Collections

let messages = vec![
    Message::Quit,
    Message::Move { x: 10, y: 20 },
    Message::Write(String::from("Hello")),
];

for msg in messages {
    msg.call();
}

• Homogeneous Collection: All elements share the same enum type.
• No Boxing Needed: If the variants fit in a reasonable amount of space, there’s no need to introduce additional indirection with a smart pointer.

10.8.2 Passing Enums to Functions

You can pass enums to functions just like any other type:

fn handle_message(msg: Message) {
    msg.call();
}

fn main() {
    let msg = Message::ChangeColor(255, 0, 0);
    handle_message(msg);
}