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use crate::{Cons, HList, Nil};
/// Merge two heterogenous lists into a single heterogenous list of pairs.
pub trait Zip<Other>: HList
where
Other: HList,
{
/// Type of new heterogenous list after merging.
type Output: HList;
/// Merges, or 'zips up' two heterogenous lists into a single heterogenous list of pairs.
///
/// It returns a new heterogenous list where the first element comes from the first list,
/// and the second element comes from the second list.
///
/// In other words, it zips two lists together, into a single one.
///
/// # Examples
///
/// ```
/// use hlist2::{hlist, ops::Zip};
///
/// let first = hlist![1, 2, 3];
/// let second = hlist![4, 5, 6];
///
/// let zipped = first.zip(second);
/// assert_eq!(zipped, hlist![(1, 4), (2, 5), (3, 6)]);
/// ```
fn zip(self, other: Other) -> Self::Output;
}
impl Zip<Nil> for Nil {
type Output = Nil;
fn zip(self, _: Nil) -> Self::Output {
self
}
}
impl<Head, Tail, OHead, OTail> Zip<Cons<OHead, OTail>> for Cons<Head, Tail>
where
Tail: Zip<OTail>,
OTail: HList,
{
type Output = Cons<(Head, OHead), Tail::Output>;
fn zip(self, other: Cons<OHead, OTail>) -> Self::Output {
let Cons(head, tail) = self;
let Cons(other_head, other_tail) = other;
let head = (head, other_head);
let tail = tail.zip(other_tail);
Cons(head, tail)
}
}