/rust/registry/src/index.crates.io-1949cf8c6b5b557f/rayon-1.11.0/src/iter/once.rs

Source
use crate::iter::plumbing::*;
use crate::iter::*;

/// Creates a parallel iterator that produces an element exactly once.
///
/// This admits no parallelism on its own, but it could be chained to existing
/// parallel iterators to extend their contents, or otherwise used for any code
/// that deals with generic parallel iterators.
///
/// # Examples
///
/// ```
/// use rayon::prelude::*;
/// use rayon::iter::once;
///
/// let pi = (0..1234).into_par_iter()
///     .chain(once(-1))
///     .chain(1234..10_000);
///
/// assert_eq!(pi.clone().count(), 10_001);
/// assert_eq!(pi.clone().filter(|&x| x < 0).count(), 1);
/// assert_eq!(pi.position_any(|x| x < 0), Some(1234));
/// ```
pub fn once<T: Send>(item: T) -> Once<T> {
    Once { item }
}

/// Iterator adaptor for [the `once()` function].
///
/// [the `once()` function]: once()
#[derive(Clone, Debug)]
pub struct Once<T> {
    item: T,
}

impl<T: Send> ParallelIterator for Once<T> {
    type Item = T;

    fn drive_unindexed<C>(self, consumer: C) -> C::Result
    where
        C: UnindexedConsumer<Self::Item>,
    {
        self.drive(consumer)
    }

    fn opt_len(&self) -> Option<usize> {
        Some(1)
    }
}

impl<T: Send> IndexedParallelIterator for Once<T> {
    fn drive<C>(self, consumer: C) -> C::Result
    where
        C: Consumer<Self::Item>,
    {
        consumer.into_folder().consume(self.item).complete()
    }

    fn len(&self) -> usize {
        1
    }

    fn with_producer<CB>(self, callback: CB) -> CB::Output
    where
        CB: ProducerCallback<Self::Item>,
    {
        // Let `OptionProducer` handle it.
        Some(self.item).into_par_iter().with_producer(callback)
    }
}

Coverage Report

Created: 2026-03-31 07:09

Line	Count	Source
1		use crate::iter::plumbing::*;
2		use crate::iter::*;
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	0	pub fn once<T: Send>(item: T) -> Once<T> {
25	0	Once { item }
26	0	} Unexecuted instantiation: rayon::iter::once::once::<i8> Unexecuted instantiation: rayon::iter::once::once::<u8> Unexecuted instantiation: rayon::iter::once::once::<isize> Unexecuted instantiation: rayon::iter::once::once::<usize> Unexecuted instantiation: rayon::iter::once::once::<i32> Unexecuted instantiation: rayon::iter::once::once::<u32> Unexecuted instantiation: rayon::iter::once::once::<i128> Unexecuted instantiation: rayon::iter::once::once::<u128> Unexecuted instantiation: rayon::iter::once::once::<i16> Unexecuted instantiation: rayon::iter::once::once::<u16> Unexecuted instantiation: rayon::iter::once::once::<i64> Unexecuted instantiation: rayon::iter::once::once::<u64>
27
28		/// Iterator adaptor for [the `once()` function].
29		///
30		/// [the `once()` function]: once()
31		#[derive(Clone, Debug)]
32		pub struct Once<T> {
33		item: T,
34		}
35
36		impl<T: Send> ParallelIterator for Once<T> {
37		type Item = T;
38
39	0	fn drive_unindexed<C>(self, consumer: C) -> C::Result
40	0	where
41	0	C: UnindexedConsumer<Self::Item>,
42		{
43	0	self.drive(consumer)
44	0	}
45
46	0	fn opt_len(&self) -> Option<usize> {
47	0	Some(1)
48	0	} Unexecuted instantiation: <rayon::iter::once::Once<i8> as rayon::iter::ParallelIterator>::opt_len Unexecuted instantiation: <rayon::iter::once::Once<u8> as rayon::iter::ParallelIterator>::opt_len Unexecuted instantiation: <rayon::iter::once::Once<isize> as rayon::iter::ParallelIterator>::opt_len Unexecuted instantiation: <rayon::iter::once::Once<usize> as rayon::iter::ParallelIterator>::opt_len Unexecuted instantiation: <rayon::iter::once::Once<i32> as rayon::iter::ParallelIterator>::opt_len Unexecuted instantiation: <rayon::iter::once::Once<u32> as rayon::iter::ParallelIterator>::opt_len Unexecuted instantiation: <rayon::iter::once::Once<i128> as rayon::iter::ParallelIterator>::opt_len Unexecuted instantiation: <rayon::iter::once::Once<u128> as rayon::iter::ParallelIterator>::opt_len Unexecuted instantiation: <rayon::iter::once::Once<i16> as rayon::iter::ParallelIterator>::opt_len Unexecuted instantiation: <rayon::iter::once::Once<u16> as rayon::iter::ParallelIterator>::opt_len Unexecuted instantiation: <rayon::iter::once::Once<i64> as rayon::iter::ParallelIterator>::opt_len Unexecuted instantiation: <rayon::iter::once::Once<u64> as rayon::iter::ParallelIterator>::opt_len
49		}
50
51		impl<T: Send> IndexedParallelIterator for Once<T> {
52	0	fn drive<C>(self, consumer: C) -> C::Result
53	0	where
54	0	C: Consumer<Self::Item>,
55		{
56	0	consumer.into_folder().consume(self.item).complete()
57	0	}
58
59	0	fn len(&self) -> usize {
60	0	1
61	0	}
62
63	0	fn with_producer<CB>(self, callback: CB) -> CB::Output
64	0	where
65	0	CB: ProducerCallback<Self::Item>,
66		{
67		// Let `OptionProducer` handle it.
68	0	Some(self.item).into_par_iter().with_producer(callback)
69	0	}
70		}