vendor/itertools-0.8.2/src/exactly_one_err.rs

   1 use std::iter::ExactSizeIterator;
   2
   3 use size_hint;
   4
   5 /// Iterator returned for the error case of `IterTools::exactly_one()`
   6 /// This iterator yields exactly the same elements as the input iterator.
   7 ///
   8 /// During the execution of exactly_one the iterator must be mutated.  This wrapper
   9 /// effectively "restores" the state of the input iterator when it's handed back.
  10 ///
  11 /// This is very similar to PutBackN except this iterator only supports 0-2 elements and does not
  12 /// use a `Vec`.
  13 #[derive(Debug, Clone)]
  14 pub struct ExactlyOneError<I>
  15 where
  16     I: Iterator,
  17 {
  18     first_two: (Option<I::Item>, Option<I::Item>),
  19     inner: I,
  20 }
  21
  22 impl<I> ExactlyOneError<I>
  23 where
  24     I: Iterator,
  25 {
  26     /// Creates a new `ExactlyOneErr` iterator.
  27     pub(crate) fn new(first_two: (Option<I::Item>, Option<I::Item>), inner: I) -> Self {
  28         Self { first_two, inner }
  29     }
  30 }
  31
  32 impl<I> Iterator for ExactlyOneError<I>
  33 where
  34     I: Iterator,
  35 {
  36     type Item = I::Item;
  37
  38     fn next(&mut self) -> Option<Self::Item> {
  39         self.first_two
  40             .0
  41             .take()
  42             .or_else(|| self.first_two.1.take())
  43             .or_else(|| self.inner.next())
  44     }
  45
  46     fn size_hint(&self) -> (usize, Option<usize>) {
  47         let mut additional_len = 0;
  48         if self.first_two.0.is_some() {
  49             additional_len += 1;
  50         }
  51         if self.first_two.1.is_some() {
  52             additional_len += 1;
  53         }
  54         size_hint::add_scalar(self.inner.size_hint(), additional_len)
  55     }
  56 }
  57
  58 impl<I> ExactSizeIterator for ExactlyOneError<I> where I: ExactSizeIterator {}