1use crate::size_hint;
2use std::iter::{Fuse, FusedIterator};
3
4/// An iterator adaptor that pads a sequence to a minimum length by filling
5/// missing elements using a closure.
6///
7/// Iterator element type is `I::Item`.
8///
9/// See [`.pad_using()`](crate::Itertools::pad_using) for more information.
10#[derive(Clone)]
11#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
12pub struct PadUsing<I, F> {
13 iter: Fuse<I>,
14 min: usize,
15 pos: usize,
16 filler: F,
17}
18
19impl<I, F> std::fmt::Debug for PadUsing<I, F>
20where
21 I: std::fmt::Debug,
22{
23 debug_fmt_fields!(PadUsing, iter, min, pos);
24}
25
26/// Create a new `PadUsing` iterator.
27pub fn pad_using<I, F>(iter: I, min: usize, filler: F) -> PadUsing<I, F>
28where
29 I: Iterator,
30 F: FnMut(usize) -> I::Item,
31{
32 PadUsing {
33 iter: iter.fuse(),
34 min,
35 pos: 0,
36 filler,
37 }
38}
39
40impl<I, F> Iterator for PadUsing<I, F>
41where
42 I: Iterator,
43 F: FnMut(usize) -> I::Item,
44{
45 type Item = I::Item;
46
47 #[inline]
48 fn next(&mut self) -> Option<Self::Item> {
49 match self.iter.next() {
50 None => {
51 if self.pos < self.min {
52 let e = Some((self.filler)(self.pos));
53 self.pos += 1;
54 e
55 } else {
56 None
57 }
58 }
59 e => {
60 self.pos += 1;
61 e
62 }
63 }
64 }
65
66 fn size_hint(&self) -> (usize, Option<usize>) {
67 let tail = self.min.saturating_sub(self.pos);
68 size_hint::max(self.iter.size_hint(), (tail, Some(tail)))
69 }
70
71 fn fold<B, G>(self, mut init: B, mut f: G) -> B
72 where
73 G: FnMut(B, Self::Item) -> B,
74 {
75 let mut pos = self.pos;
76 init = self.iter.fold(init, |acc, item| {
77 pos += 1;
78 f(acc, item)
79 });
80 (pos..self.min).map(self.filler).fold(init, f)
81 }
82}
83
84impl<I, F> DoubleEndedIterator for PadUsing<I, F>
85where
86 I: DoubleEndedIterator + ExactSizeIterator,
87 F: FnMut(usize) -> I::Item,
88{
89 fn next_back(&mut self) -> Option<Self::Item> {
90 if self.min == 0 {
91 self.iter.next_back()
92 } else if self.iter.len() >= self.min {
93 self.min -= 1;
94 self.iter.next_back()
95 } else {
96 self.min -= 1;
97 Some((self.filler)(self.min))
98 }
99 }
100
101 fn rfold<B, G>(self, mut init: B, mut f: G) -> B
102 where
103 G: FnMut(B, Self::Item) -> B,
104 {
105 init = (self.iter.len()..self.min)
106 .map(self.filler)
107 .rfold(init, &mut f);
108 self.iter.rfold(init, f)
109 }
110}
111
112impl<I, F> ExactSizeIterator for PadUsing<I, F>
113where
114 I: ExactSizeIterator,
115 F: FnMut(usize) -> I::Item,
116{
117}
118
119impl<I, F> FusedIterator for PadUsing<I, F>
120where
121 I: FusedIterator,
122 F: FnMut(usize) -> I::Item,
123{
124}
125