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1 | use crate::iter::plumbing::*; |
2 | use crate::iter::*; | |
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3 | |
4 | /// Creates a parallel iterator that produces an element exactly once. | |
5 | /// | |
6 | /// This admits no parallelism on its own, but it could be chained to existing | |
7 | /// parallel iterators to extend their contents, or otherwise used for any code | |
8 | /// that deals with generic parallel iterators. | |
9 | /// | |
10 | /// # Examples | |
11 | /// | |
12 | /// ``` | |
13 | /// use rayon::prelude::*; | |
14 | /// use rayon::iter::once; | |
15 | /// | |
16 | /// let pi = (0..1234).into_par_iter() | |
17 | /// .chain(once(-1)) | |
18 | /// .chain(1234..10_000); | |
19 | /// | |
20 | /// assert_eq!(pi.clone().count(), 10_001); | |
21 | /// assert_eq!(pi.clone().filter(|&x| x < 0).count(), 1); | |
22 | /// assert_eq!(pi.position_any(|x| x < 0), Some(1234)); | |
23 | /// ``` | |
24 | pub fn once<T: Send>(item: T) -> Once<T> { | |
e74abb32 | 25 | Once { item } |
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26 | } |
27 | ||
28 | /// Iterator adaptor for [the `once()` function](fn.once.html). | |
29 | #[derive(Clone, Debug)] | |
30 | pub struct Once<T: Send> { | |
31 | item: T, | |
32 | } | |
33 | ||
34 | impl<T: Send> ParallelIterator for Once<T> { | |
35 | type Item = T; | |
36 | ||
37 | fn drive_unindexed<C>(self, consumer: C) -> C::Result | |
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38 | where |
39 | C: UnindexedConsumer<Self::Item>, | |
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40 | { |
41 | self.drive(consumer) | |
42 | } | |
43 | ||
44 | fn opt_len(&self) -> Option<usize> { | |
45 | Some(1) | |
46 | } | |
47 | } | |
48 | ||
49 | impl<T: Send> IndexedParallelIterator for Once<T> { | |
50 | fn drive<C>(self, consumer: C) -> C::Result | |
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51 | where |
52 | C: Consumer<Self::Item>, | |
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53 | { |
54 | consumer.into_folder().consume(self.item).complete() | |
55 | } | |
56 | ||
57 | fn len(&self) -> usize { | |
58 | 1 | |
59 | } | |
60 | ||
61 | fn with_producer<CB>(self, callback: CB) -> CB::Output | |
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62 | where |
63 | CB: ProducerCallback<Self::Item>, | |
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64 | { |
65 | // Let `OptionProducer` handle it. | |
66 | Some(self.item).into_par_iter().with_producer(callback) | |
67 | } | |
68 | } |