Cycle over a known set of values.

Author: felipesere

src/stream/cycle.rs

@@ -0,0 +1,62 @@
+use std::pin::Pin;
+
+use pin_project_lite::pin_project;
+
+use crate::stream::Stream;
+use crate::task::{Context, Poll};
+
+pin_project! {
+    /// A stream that will repeatedly yield the same list of elements
+    pub struct Cycle<T> {
+        source: Vec<T>,
+        index: usize,
+        len: usize,
+    }
+}
+
+impl<T: Copy> Stream for Cycle<T> {
+    type Item = T;
+
+    fn poll_next(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let value = self.source[self.index];
+
+        let next = self.index + 1;
+
+        if next >= self.len {
+            self.as_mut().index = 0;
+        } else {
+            self.as_mut().index = next;
+        }
+
+        Poll::Ready(Some(value))
+    }
+}
+
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// # async_std::task::block_on(async {
+/// #
+/// use async_std::prelude::*;
+/// use async_std::stream;
+///
+/// let mut s = stream::cycle(vec![1,2,3]);
+///
+/// assert_eq!(s.next().await, Some(1));
+/// assert_eq!(s.next().await, Some(2));
+/// assert_eq!(s.next().await, Some(3));
+/// assert_eq!(s.next().await, Some(1));
+/// assert_eq!(s.next().await, Some(2));
+/// #
+/// # })
+/// ```
+pub fn cycle<T: Copy>(source: Vec<T>) -> impl Stream<Item = T> {
+    let len = source.len();
+    Cycle {
+        source,
+        index: 0,
+        len,
+    }
+}

src/stream/mod.rs

@@ -300,6 +300,7 @@
 //! [`take`]: trait.Stream.html#method.take
 //! [`min`]: trait.Stream.html#method.min
 
+pub use cycle::{cycle, Cycle};
 pub use empty::{empty, Empty};
 pub use from_fn::{from_fn, FromFn};
 pub use from_iter::{from_iter, FromIter};
@@ -312,6 +313,7 @@ pub use stream::{
 
 pub(crate) mod stream;
 
+mod cycle;
 mod empty;
 mod from_fn;
 mod from_iter;

src/stream/stream/cycle.rs

@@ -24,10 +24,11 @@
 mod all;
 mod any;
 mod chain;
-mod enumerate;
+mod cmp;
 mod cycle;
 mod copied;
 mod cmp;
+mod enumerate;
 mod eq;
 mod filter;
 mod filter_map;