1use super::plumbing::*;
2use super::*;
3use crate::math::div_round_up;
4use std::iter;
5use std::usize;
6
7/// `StepBy` is an iterator that skips `n` elements between each yield, where `n` is the given step.
8/// This struct is created by the [`step_by()`] method on [`IndexedParallelIterator`]
9///
10/// [`step_by()`]: trait.IndexedParallelIterator.html#method.step_by
11/// [`IndexedParallelIterator`]: trait.IndexedParallelIterator.html
12#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
13#[derive(Debug, Clone)]
14pub struct StepBy<I: IndexedParallelIterator> {
15 base: I,
16 step: usize,
17}
18
19impl<I> StepBy<I>
20where
21 I: IndexedParallelIterator,
22{
23 /// Creates a new `StepBy` iterator.
24 pub(super) fn new(base: I, step: usize) -> Self {
25 StepBy { base, step }
26 }
27}
28
29impl<I> ParallelIterator for StepBy<I>
30where
31 I: IndexedParallelIterator,
32{
33 type Item = I::Item;
34
35 fn drive_unindexed<C>(self, consumer: C) -> C::Result
36 where
37 C: UnindexedConsumer<Self::Item>,
38 {
39 bridge(self, consumer)
40 }
41
42 fn opt_len(&self) -> Option<usize> {
43 Some(self.len())
44 }
45}
46
47impl<I> IndexedParallelIterator for StepBy<I>
48where
49 I: IndexedParallelIterator,
50{
51 fn drive<C: Consumer<Self::Item>>(self, consumer: C) -> C::Result {
52 bridge(self, consumer)
53 }
54
55 fn len(&self) -> usize {
56 div_round_up(self.base.len(), self.step)
57 }
58
59 fn with_producer<CB>(self, callback: CB) -> CB::Output
60 where
61 CB: ProducerCallback<Self::Item>,
62 {
63 let len = self.base.len();
64 return self.base.with_producer(Callback {
65 callback,
66 step: self.step,
67 len,
68 });
69
70 struct Callback<CB> {
71 callback: CB,
72 step: usize,
73 len: usize,
74 }
75
76 impl<T, CB> ProducerCallback<T> for Callback<CB>
77 where
78 CB: ProducerCallback<T>,
79 {
80 type Output = CB::Output;
81 fn callback<P>(self, base: P) -> CB::Output
82 where
83 P: Producer<Item = T>,
84 {
85 let producer = StepByProducer {
86 base,
87 step: self.step,
88 len: self.len,
89 };
90 self.callback.callback(producer)
91 }
92 }
93 }
94}
95
96/// ////////////////////////////////////////////////////////////////////////
97/// Producer implementation
98
99struct StepByProducer<P> {
100 base: P,
101 step: usize,
102 len: usize,
103}
104
105impl<P> Producer for StepByProducer<P>
106where
107 P: Producer,
108{
109 type Item = P::Item;
110 type IntoIter = iter::StepBy<P::IntoIter>;
111
112 fn into_iter(self) -> Self::IntoIter {
113 self.base.into_iter().step_by(self.step)
114 }
115
116 fn split_at(self, index: usize) -> (Self, Self) {
117 let elem_index = Ord::min(index * self.step, self.len);
118
119 let (left, right) = self.base.split_at(elem_index);
120 (
121 StepByProducer {
122 base: left,
123 step: self.step,
124 len: elem_index,
125 },
126 StepByProducer {
127 base: right,
128 step: self.step,
129 len: self.len - elem_index,
130 },
131 )
132 }
133
134 fn min_len(&self) -> usize {
135 div_round_up(self.base.min_len(), self.step)
136 }
137
138 fn max_len(&self) -> usize {
139 self.base.max_len() / self.step
140 }
141}
142