1use super::plumbing::*;
2use super::*;
3use rayon_core::join;
4use std::iter;
5
6/// `Chain` is an iterator that joins `b` after `a` in one continuous iterator.
7/// This struct is created by the [`chain()`] method on [`ParallelIterator`]
8///
9/// [`chain()`]: trait.ParallelIterator.html#method.chain
10/// [`ParallelIterator`]: trait.ParallelIterator.html
11#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
12#[derive(Debug, Clone)]
13pub struct Chain<A, B>
14where
15 A: ParallelIterator,
16 B: ParallelIterator<Item = A::Item>,
17{
18 a: A,
19 b: B,
20}
21
22impl<A, B> Chain<A, B>
23where
24 A: ParallelIterator,
25 B: ParallelIterator<Item = A::Item>,
26{
27 /// Creates a new `Chain` iterator.
28 pub(super) fn new(a: A, b: B) -> Self {
29 Chain { a, b }
30 }
31}
32
33impl<A, B> ParallelIterator for Chain<A, B>
34where
35 A: ParallelIterator,
36 B: ParallelIterator<Item = A::Item>,
37{
38 type Item = A::Item;
39
40 fn drive_unindexed<C>(self, consumer: C) -> C::Result
41 where
42 C: UnindexedConsumer<Self::Item>,
43 {
44 let Chain { a, b } = self;
45
46 // If we returned a value from our own `opt_len`, then the collect consumer in particular
47 // will balk at being treated like an actual `UnindexedConsumer`. But when we do know the
48 // length, we can use `Consumer::split_at` instead, and this is still harmless for other
49 // truly-unindexed consumers too.
50 let (left, right, reducer) = if let Some(len) = a.opt_len() {
51 consumer.split_at(len)
52 } else {
53 let reducer = consumer.to_reducer();
54 (consumer.split_off_left(), consumer, reducer)
55 };
56
57 let (a, b) = join(|| a.drive_unindexed(left), || b.drive_unindexed(right));
58 reducer.reduce(a, b)
59 }
60
61 fn opt_len(&self) -> Option<usize> {
62 self.a.opt_len()?.checked_add(self.b.opt_len()?)
63 }
64}
65
66impl<A, B> IndexedParallelIterator for Chain<A, B>
67where
68 A: IndexedParallelIterator,
69 B: IndexedParallelIterator<Item = A::Item>,
70{
71 fn drive<C>(self, consumer: C) -> C::Result
72 where
73 C: Consumer<Self::Item>,
74 {
75 let Chain { a, b } = self;
76 let (left, right, reducer) = consumer.split_at(a.len());
77 let (a, b) = join(|| a.drive(left), || b.drive(right));
78 reducer.reduce(a, b)
79 }
80
81 fn len(&self) -> usize {
82 self.a.len().checked_add(self.b.len()).expect("overflow")
83 }
84
85 fn with_producer<CB>(self, callback: CB) -> CB::Output
86 where
87 CB: ProducerCallback<Self::Item>,
88 {
89 let a_len = self.a.len();
90 return self.a.with_producer(CallbackA {
91 callback,
92 a_len,
93 b: self.b,
94 });
95
96 struct CallbackA<CB, B> {
97 callback: CB,
98 a_len: usize,
99 b: B,
100 }
101
102 impl<CB, B> ProducerCallback<B::Item> for CallbackA<CB, B>
103 where
104 B: IndexedParallelIterator,
105 CB: ProducerCallback<B::Item>,
106 {
107 type Output = CB::Output;
108
109 fn callback<A>(self, a_producer: A) -> Self::Output
110 where
111 A: Producer<Item = B::Item>,
112 {
113 self.b.with_producer(CallbackB {
114 callback: self.callback,
115 a_len: self.a_len,
116 a_producer,
117 })
118 }
119 }
120
121 struct CallbackB<CB, A> {
122 callback: CB,
123 a_len: usize,
124 a_producer: A,
125 }
126
127 impl<CB, A> ProducerCallback<A::Item> for CallbackB<CB, A>
128 where
129 A: Producer,
130 CB: ProducerCallback<A::Item>,
131 {
132 type Output = CB::Output;
133
134 fn callback<B>(self, b_producer: B) -> Self::Output
135 where
136 B: Producer<Item = A::Item>,
137 {
138 let producer = ChainProducer::new(self.a_len, self.a_producer, b_producer);
139 self.callback.callback(producer)
140 }
141 }
142 }
143}
144
145/// ////////////////////////////////////////////////////////////////////////
146
147struct ChainProducer<A, B>
148where
149 A: Producer,
150 B: Producer<Item = A::Item>,
151{
152 a_len: usize,
153 a: A,
154 b: B,
155}
156
157impl<A, B> ChainProducer<A, B>
158where
159 A: Producer,
160 B: Producer<Item = A::Item>,
161{
162 fn new(a_len: usize, a: A, b: B) -> Self {
163 ChainProducer { a_len, a, b }
164 }
165}
166
167impl<A, B> Producer for ChainProducer<A, B>
168where
169 A: Producer,
170 B: Producer<Item = A::Item>,
171{
172 type Item = A::Item;
173 type IntoIter = ChainSeq<A::IntoIter, B::IntoIter>;
174
175 fn into_iter(self) -> Self::IntoIter {
176 ChainSeq::new(self.a.into_iter(), self.b.into_iter())
177 }
178
179 fn min_len(&self) -> usize {
180 Ord::max(self.a.min_len(), self.b.min_len())
181 }
182
183 fn max_len(&self) -> usize {
184 Ord::min(self.a.max_len(), self.b.max_len())
185 }
186
187 fn split_at(self, index: usize) -> (Self, Self) {
188 if index <= self.a_len {
189 let a_rem = self.a_len - index;
190 let (a_left, a_right) = self.a.split_at(index);
191 let (b_left, b_right) = self.b.split_at(0);
192 (
193 ChainProducer::new(index, a_left, b_left),
194 ChainProducer::new(a_rem, a_right, b_right),
195 )
196 } else {
197 let (a_left, a_right) = self.a.split_at(self.a_len);
198 let (b_left, b_right) = self.b.split_at(index - self.a_len);
199 (
200 ChainProducer::new(self.a_len, a_left, b_left),
201 ChainProducer::new(0, a_right, b_right),
202 )
203 }
204 }
205
206 fn fold_with<F>(self, mut folder: F) -> F
207 where
208 F: Folder<A::Item>,
209 {
210 folder = self.a.fold_with(folder);
211 if folder.full() {
212 folder
213 } else {
214 self.b.fold_with(folder)
215 }
216 }
217}
218
219/// ////////////////////////////////////////////////////////////////////////
220/// Wrapper for Chain to implement ExactSizeIterator
221
222struct ChainSeq<A, B> {
223 chain: iter::Chain<A, B>,
224}
225
226impl<A, B> ChainSeq<A, B> {
227 fn new(a: A, b: B) -> ChainSeq<A, B>
228 where
229 A: ExactSizeIterator,
230 B: ExactSizeIterator<Item = A::Item>,
231 {
232 ChainSeq { chain: a.chain(b) }
233 }
234}
235
236impl<A, B> Iterator for ChainSeq<A, B>
237where
238 A: Iterator,
239 B: Iterator<Item = A::Item>,
240{
241 type Item = A::Item;
242
243 fn next(&mut self) -> Option<Self::Item> {
244 self.chain.next()
245 }
246
247 fn size_hint(&self) -> (usize, Option<usize>) {
248 self.chain.size_hint()
249 }
250}
251
252impl<A, B> ExactSizeIterator for ChainSeq<A, B>
253where
254 A: ExactSizeIterator,
255 B: ExactSizeIterator<Item = A::Item>,
256{
257}
258
259impl<A, B> DoubleEndedIterator for ChainSeq<A, B>
260where
261 A: DoubleEndedIterator,
262 B: DoubleEndedIterator<Item = A::Item>,
263{
264 fn next_back(&mut self) -> Option<Self::Item> {
265 self.chain.next_back()
266 }
267}
268