Initial import of rayon-1.5.0. am: 041839ceab am: d836dd6404 am: 7522a9ba00

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/rayon/+/1622436

Change-Id: I94b0e06d9da131d6f98db436ad1a178dfff2ec90

1 files changed, 104 insertions, 0 deletions

diff --git a/src/iter/empty.rs b/src/iter/empty.rs
new file mode 100644
index 0000000..85a2e5f
--- /dev/null
+++ b/src/iter/empty.rs
@@ -0,0 +1,104 @@
+use crate::iter::plumbing::*;
+use crate::iter::*;
+
+use std::fmt;
+use std::marker::PhantomData;
+
+/// Creates a parallel iterator that produces nothing.
+///
+/// This admits no parallelism on its own, but it could be used for code that
+/// deals with generic parallel iterators.
+///
+/// # Examples
+///
+/// ```
+/// use rayon::prelude::*;
+/// use rayon::iter::empty;
+///
+/// let pi = (0..1234).into_par_iter()
+///     .chain(empty())
+///     .chain(1234..10_000);
+///
+/// assert_eq!(pi.count(), 10_000);
+/// ```
+pub fn empty<T: Send>() -> Empty<T> {
+    Empty {
+        marker: PhantomData,
+    }
+}
+
+/// Iterator adaptor for [the `empty()` function](fn.empty.html).
+pub struct Empty<T: Send> {
+    marker: PhantomData<T>,
+}
+
+impl<T: Send> Clone for Empty<T> {
+    fn clone(&self) -> Self {
+        empty()
+    }
+}
+
+impl<T: Send> fmt::Debug for Empty<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad("Empty")
+    }
+}
+
+impl<T: Send> ParallelIterator for Empty<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(0)
+    }
+}
+
+impl<T: Send> IndexedParallelIterator for Empty<T> {
+    fn drive<C>(self, consumer: C) -> C::Result
+    where
+        C: Consumer<Self::Item>,
+    {
+        consumer.into_folder().complete()
+    }
+
+    fn len(&self) -> usize {
+        0
+    }
+
+    fn with_producer<CB>(self, callback: CB) -> CB::Output
+    where
+        CB: ProducerCallback<Self::Item>,
+    {
+        callback.callback(EmptyProducer(PhantomData))
+    }
+}
+
+/// Private empty producer
+struct EmptyProducer<T: Send>(PhantomData<T>);
+
+impl<T: Send> Producer for EmptyProducer<T> {
+    type Item = T;
+    type IntoIter = std::iter::Empty<T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        std::iter::empty()
+    }
+
+    fn split_at(self, index: usize) -> (Self, Self) {
+        debug_assert_eq!(index, 0);
+        (self, EmptyProducer(PhantomData))
+    }
+
+    fn fold_with<F>(self, folder: F) -> F
+    where
+        F: Folder<Self::Item>,
+    {
+        folder
+    }
+}