1 use std::iter::FusedIterator;
2
3 /// An iterator that produces *n* repetitions of an element.
4 ///
5 /// See [`repeat_n()`](crate::repeat_n) for more information.
6 #[must_use = "iterators are lazy and do nothing unless consumed"]
7 #[derive(Clone, Debug)]
8 pub struct RepeatN<A> {
9 pub(crate) elt: Option<A>,
10 n: usize,
11 }
12
13 /// Create an iterator that produces `n` repetitions of `element`.
repeat_n<A>(element: A, n: usize) -> RepeatN<A> where A: Clone,14 pub fn repeat_n<A>(element: A, n: usize) -> RepeatN<A>
15 where
16 A: Clone,
17 {
18 if n == 0 {
19 RepeatN { elt: None, n }
20 } else {
21 RepeatN {
22 elt: Some(element),
23 n,
24 }
25 }
26 }
27
28 impl<A> Iterator for RepeatN<A>
29 where
30 A: Clone,
31 {
32 type Item = A;
33
next(&mut self) -> Option<Self::Item>34 fn next(&mut self) -> Option<Self::Item> {
35 if self.n > 1 {
36 self.n -= 1;
37 self.elt.as_ref().cloned()
38 } else {
39 self.n = 0;
40 self.elt.take()
41 }
42 }
43
size_hint(&self) -> (usize, Option<usize>)44 fn size_hint(&self) -> (usize, Option<usize>) {
45 (self.n, Some(self.n))
46 }
47
fold<B, F>(self, mut init: B, mut f: F) -> B where F: FnMut(B, Self::Item) -> B,48 fn fold<B, F>(self, mut init: B, mut f: F) -> B
49 where
50 F: FnMut(B, Self::Item) -> B,
51 {
52 match self {
53 Self { elt: Some(elt), n } => {
54 debug_assert!(n > 0);
55 init = (1..n).map(|_| elt.clone()).fold(init, &mut f);
56 f(init, elt)
57 }
58 _ => init,
59 }
60 }
61 }
62
63 impl<A> DoubleEndedIterator for RepeatN<A>
64 where
65 A: Clone,
66 {
67 #[inline]
next_back(&mut self) -> Option<Self::Item>68 fn next_back(&mut self) -> Option<Self::Item> {
69 self.next()
70 }
71
72 #[inline]
rfold<B, F>(self, init: B, f: F) -> B where F: FnMut(B, Self::Item) -> B,73 fn rfold<B, F>(self, init: B, f: F) -> B
74 where
75 F: FnMut(B, Self::Item) -> B,
76 {
77 self.fold(init, f)
78 }
79 }
80
81 impl<A> ExactSizeIterator for RepeatN<A> where A: Clone {}
82
83 impl<A> FusedIterator for RepeatN<A> where A: Clone {}
84