rayon/iter/
empty.rs

1use crate::iter::plumbing::*;
2use crate::iter::*;
3
4use std::fmt;
5use std::marker::PhantomData;
6
7/// Creates a parallel iterator that produces nothing.
8///
9/// This admits no parallelism on its own, but it could be used for code that
10/// deals with generic parallel iterators.
11///
12/// # Examples
13///
14/// ```
15/// use rayon::prelude::*;
16/// use rayon::iter::empty;
17///
18/// let pi = (0..1234).into_par_iter()
19///     .chain(empty())
20///     .chain(1234..10_000);
21///
22/// assert_eq!(pi.count(), 10_000);
23/// ```
24pub fn empty<T: Send>() -> Empty<T> {
25    Empty {
26        marker: PhantomData,
27    }
28}
29
30/// Iterator adaptor for [the `empty()` function](fn.empty.html).
31pub struct Empty<T: Send> {
32    marker: PhantomData<T>,
33}
34
35impl<T: Send> Clone for Empty<T> {
36    fn clone(&self) -> Self {
37        empty()
38    }
39}
40
41impl<T: Send> fmt::Debug for Empty<T> {
42    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
43        f.pad("Empty")
44    }
45}
46
47impl<T: Send> ParallelIterator for Empty<T> {
48    type Item = T;
49
50    fn drive_unindexed<C>(self, consumer: C) -> C::Result
51    where
52        C: UnindexedConsumer<Self::Item>,
53    {
54        self.drive(consumer)
55    }
56
57    fn opt_len(&self) -> Option<usize> {
58        Some(0)
59    }
60}
61
62impl<T: Send> IndexedParallelIterator for Empty<T> {
63    fn drive<C>(self, consumer: C) -> C::Result
64    where
65        C: Consumer<Self::Item>,
66    {
67        consumer.into_folder().complete()
68    }
69
70    fn len(&self) -> usize {
71        0
72    }
73
74    fn with_producer<CB>(self, callback: CB) -> CB::Output
75    where
76        CB: ProducerCallback<Self::Item>,
77    {
78        callback.callback(EmptyProducer(PhantomData))
79    }
80}
81
82/// Private empty producer
83struct EmptyProducer<T: Send>(PhantomData<T>);
84
85impl<T: Send> Producer for EmptyProducer<T> {
86    type Item = T;
87    type IntoIter = std::iter::Empty<T>;
88
89    fn into_iter(self) -> Self::IntoIter {
90        std::iter::empty()
91    }
92
93    fn split_at(self, index: usize) -> (Self, Self) {
94        debug_assert_eq!(index, 0);
95        (self, EmptyProducer(PhantomData))
96    }
97
98    fn fold_with<F>(self, folder: F) -> F
99    where
100        F: Folder<Self::Item>,
101    {
102        folder
103    }
104}
rayon/iter/empty.rs

rayon/iter/
empty.rs
