vendor/itertools-0.9.0/src/zip_longest.rs

   1 use std::cmp::Ordering::{Equal, Greater, Less};
   2 use super::size_hint;
   3 use std::iter::Fuse;
   4
   5 use crate::either_or_both::EitherOrBoth;
   6
   7 // ZipLongest originally written by SimonSapin,
   8 // and dedicated to itertools https://github.com/rust-lang/rust/pull/19283
   9
  10 /// An iterator which iterates two other iterators simultaneously
  11 ///
  12 /// This iterator is *fused*.
  13 ///
  14 /// See [`.zip_longest()`](../trait.Itertools.html#method.zip_longest) for more information.
  15 #[derive(Clone, Debug)]
  16 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
  17 pub struct ZipLongest<T, U> {
  18     a: Fuse<T>,
  19     b: Fuse<U>,
  20 }
  21
  22 /// Create a new `ZipLongest` iterator.
  23 pub fn zip_longest<T, U>(a: T, b: U) -> ZipLongest<T, U>
  24     where T: Iterator,
  25           U: Iterator
  26 {
  27     ZipLongest {
  28         a: a.fuse(),
  29         b: b.fuse(),
  30     }
  31 }
  32
  33 impl<T, U> Iterator for ZipLongest<T, U>
  34     where T: Iterator,
  35           U: Iterator
  36 {
  37     type Item = EitherOrBoth<T::Item, U::Item>;
  38
  39     #[inline]
  40     fn next(&mut self) -> Option<Self::Item> {
  41         match (self.a.next(), self.b.next()) {
  42             (None, None) => None,
  43             (Some(a), None) => Some(EitherOrBoth::Left(a)),
  44             (None, Some(b)) => Some(EitherOrBoth::Right(b)),
  45             (Some(a), Some(b)) => Some(EitherOrBoth::Both(a, b)),
  46         }
  47     }
  48
  49     #[inline]
  50     fn size_hint(&self) -> (usize, Option<usize>) {
  51         size_hint::max(self.a.size_hint(), self.b.size_hint())
  52     }
  53 }
  54
  55 impl<T, U> DoubleEndedIterator for ZipLongest<T, U>
  56     where T: DoubleEndedIterator + ExactSizeIterator,
  57           U: DoubleEndedIterator + ExactSizeIterator
  58 {
  59     #[inline]
  60     fn next_back(&mut self) -> Option<Self::Item> {
  61         match self.a.len().cmp(&self.b.len()) {
  62             Equal => match (self.a.next_back(), self.b.next_back()) {
  63                 (None, None) => None,
  64                 (Some(a), Some(b)) => Some(EitherOrBoth::Both(a, b)),
  65                 // These can only happen if .len() is inconsistent with .next_back()
  66                 (Some(a), None) => Some(EitherOrBoth::Left(a)),
  67                 (None, Some(b)) => Some(EitherOrBoth::Right(b)),
  68             },
  69             Greater => self.a.next_back().map(EitherOrBoth::Left),
  70             Less => self.b.next_back().map(EitherOrBoth::Right),
  71         }
  72     }
  73 }
  74
  75 impl<T, U> ExactSizeIterator for ZipLongest<T, U>
  76     where T: ExactSizeIterator,
  77           U: ExactSizeIterator
  78 {}