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-rw-r--r--third_party/rust/rayon/src/iter/once.rs68
1 files changed, 68 insertions, 0 deletions
diff --git a/third_party/rust/rayon/src/iter/once.rs b/third_party/rust/rayon/src/iter/once.rs
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+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](fn.once.html).
+#[derive(Clone, Debug)]
+pub struct Once<T: Send> {
+ 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)
+ }
+}