Rust by Example

Repeat

Macros can use + in the argument list to indicate that an argument may repeat at least once, or *, to indicate that the argument may repeat zero or more times.

In the following example, surrounding the matcher with $(...),+ will match one or more expression, separated by commas. Also note that the semicolon is optional on the last case.

// `find_min!` will calculate the minimum of any number of arguments.

macro_rules! find_min {

// Base case:

($x:expr) => ($x);

// `$x` followed by at least one `$y,`

($x:expr, $($y:expr),+) => (

// Call `find_min!` on the tail `$y`

std::cmp::min($x, find_min!($($y),+))

)

}

fn main() {

println!("{}", find_min!(1u32));

println!("{}", find_min!(1u32 + 2, 2u32));

println!("{}", find_min!(5u32, 2u32 * 3, 4u32));

}

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