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)]
10#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
11pub struct PutBackN<I: Iterator> {
12    top: Vec<I::Item>,
13    iter: I,
14}
15
16/// Create an iterator where you can put back multiple values to the front
17/// of the iteration.
18///
19/// Iterator element type is `I::Item`.
20pub fn put_back_n<I>(iterable: I) -> PutBackN<I::IntoIter>
21where
22    I: IntoIterator,
23{
24    PutBackN {
25        top: Vec::new(),
26        iter: iterable.into_iter(),
27    }
28}
29
30impl<I: Iterator> PutBackN<I> {
31    /// Puts x in front of the iterator.
32    /// The values are yielded in order of the most recently put back
33    /// values first.
34    ///
35    /// ```rust
36    /// use itertools::put_back_n;
37    ///
38    /// let mut it = put_back_n(1..5);
39    /// it.next();
40    /// it.put_back(1);
41    /// it.put_back(0);
42    ///
43    /// assert!(itertools::equal(it, 0..5));
44    /// ```
45    #[inline]
46    pub fn put_back(&mut self, x: I::Item) {
47        self.top.push(x);
48    }
49}
50
51impl<I: Iterator> Iterator for PutBackN<I> {
52    type Item = I::Item;
53    #[inline]
54    fn next(&mut self) -> Option<Self::Item> {
55        self.top.pop().or_else(|| self.iter.next())
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    fn fold<B, F>(self, mut init: B, mut f: F) -> B
64    where
65        F: FnMut(B, Self::Item) -> B,
66    {
67        init = self.top.into_iter().rfold(init, &mut f);
68        self.iter.fold(init, f)
69    }
70}
itertools/put_back_n_impl.rs

itertools/
put_back_n_impl.rs
