Example
A macro can produce different outputs against different input patterns:
/// The `sum` macro may be invoked in two ways:
///
/// sum!(iterator)
/// sum!(1234, iterator)
///
macro_rules! sum {
($iter:expr) => { // This branch handles the `sum!(iterator)` case
$iter.fold(0, |a, b| a + *b)
};
// ^ use `;` to separate each branch
($start:expr, $iter:expr) => { // This branch handles the `sum!(1234, iter)` case
$iter.fold($start, |a, b| a + *b)
};
}
fn main() {
assert_eq!(10, sum!([1, 2, 3, 4].iter()));
assert_eq!(23, sum!(6, [2, 5, 9, 1].iter()));
}
