Rust for C-Programmers

10.8 Enums in Collections and Functions

Even though enum variants may contain different data with varying sizes, they are considered a single type.

10.8.1 Storing Enums in Collections

Example:

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 are of type Message.
• No Boxing Needed: Unlike trait objects, no heap allocation is required for polymorphism.

10.8.2 Passing Enums to Functions

Functions can accept enums as parameters and handle all variants.

Example:

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

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