1 use crate::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`.
put_back_n<I>(iterable: I) -> PutBackN<I::IntoIter> where I: IntoIterator17 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]
put_back(&mut self, x: I::Item)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]
next(&mut self) -> Option<I::Item>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]
size_hint(&self) -> (usize, Option<usize>)59 fn size_hint(&self) -> (usize, Option<usize>) {
60 size_hint::add_scalar(self.iter.size_hint(), self.top.len())
61 }
62 }
63
64