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// zip!(a1,a2,a3,a4) is equivalent to:
// a1.zip(a2).zip(a3).zip(a4).map(|(((x1,x2),x3),x4)| (x1,x2,x3,x4))
macro_rules! zip {
// Entry point
([$a:expr, $b:expr, $($rest:expr),*]) => {
zip!([$($rest),*], $a.zip($b), (x,y), [x,y])
};
// Intermediate steps to build the zipped expression, the match pattern, and
// and the output tuple of the closure, using macro hygene to repeatedly
// introduce new variables named 'x'.
([$a:expr, $($rest:expr),*], $zip:expr, $pat:pat, [$($flat:expr),*]) => {
zip!([$($rest),*], $zip.zip($a), ($pat,x), [$($flat),*, x])
};
// Final step
([], $zip:expr, $pat:pat, [$($flat:expr),+]) => {
$zip.map(|$pat| ($($flat),+))
};
// Comma
([$a:expr], $zip:expr, $pat:pat, [$($flat:expr),*]) => {
zip!([$a,], $zip, $pat, [$($flat),*])
};
}
fn main() {
let p1 = vec![1i32, 2].into_iter();
let p2 = vec!["10", "20"].into_iter();
let p3 = vec![100u16, 200].into_iter();
let p4 = vec![1000i64, 2000].into_iter();
let e = zip!([p1, p2, p3, p4]).collect::<Vec<_>>();
assert_eq!(e[0], (1i32, "10", 100u16, 1000i64));
}
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