itertools/
put_back_n_impl.rs

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

itertools/
put_back_n_impl.rs
