vendor/itertools/src/put_back_n_impl.rs

   1 use size_hint;
   2
   3 /// An iterator adaptor that allows putting multiple
   4 /// items in front of the iterator.
   5 ///
   6 /// Iterator element type is `I::Item`.
   7 #[derive(Debug, Clone)]
   8 pub struct PutBackN<I: Iterator> {
   9     top: Vec<I::Item>,
  10     iter: I,
  11 }
  12
  13 /// Create an iterator where you can put back multiple values to the front
  14 /// of the iteration.
  15 ///
  16 /// Iterator element type is `I::Item`.
  17 pub fn put_back_n<I>(iterable: I) -> PutBackN<I::IntoIter>
  18     where I: IntoIterator
  19 {
  20     PutBackN {
  21         top: Vec::new(),
  22         iter: iterable.into_iter(),
  23     }
  24 }
  25
  26 impl<I: Iterator> PutBackN<I> {
  27     /// Puts x in front of the iterator.
  28     /// The values are yielded in order of the most recently put back
  29     /// values first.
  30     ///
  31     /// ```rust
  32     /// use itertools::put_back_n;
  33     ///
  34     /// let mut it = put_back_n(1..5);
  35     /// it.next();
  36     /// it.put_back(1);
  37     /// it.put_back(0);
  38     ///
  39     /// assert!(itertools::equal(it, 0..5));
  40     /// ```
  41     #[inline]
  42     pub fn put_back(&mut self, x: I::Item) {
  43         self.top.push(x);
  44     }
  45 }
  46
  47 impl<I: Iterator> Iterator for PutBackN<I> {
  48     type Item = I::Item;
  49     #[inline]
  50     fn next(&mut self) -> Option<I::Item> {
  51         if self.top.is_empty() {
  52             self.iter.next()
  53         } else {
  54             self.top.pop()
  55         }
  56     }
  57
  58     #[inline]
  59     fn size_hint(&self) -> (usize, Option<usize>) {
  60         size_hint::add_scalar(self.iter.size_hint(), self.top.len())
  61     }
  62 }
  63