How to Use Repetitions in Rust Macros ($(...),*)

Use the $( ... )* syntax to repeat a sequence of tokens zero or more times, or $( ... )+ for one or more times. Place the repetition operator immediately after the closing delimiter of the token sequence.

macro_rules! repeat {
    ($($x:expr),*) => {
        $(
            println!("Item: {}", $x);
        )*
    };
}

fn main() {
    repeat!(1, 2, 3);
}

In this example, $($x:expr),* matches a comma-separated list of expressions. The * operator repeats the pattern for every item in the list. If you need a separator other than a comma, place it inside the parentheses before the operator, like $( $x:expr; )*.

Repetitions in Rust macros let you write code that handles lists of items without writing loops manually. Think of it like a template that fills in a blank for every item you pass to it. You use * to repeat zero or more times, or + to ensure at least one item exists.