Stream::cycle implementation

examples/stream-cycle.rs

@@ -0,0 +1,25 @@
+//! Repeats given stream values and sum them
+
+#![feature(async_await)]
+
+use async_std::io;
+use async_std::prelude::*;
+use async_std::stream;
+use async_std::task;
+
+fn main() -> io::Result<()> {
+    task::block_on(async {
+        let mut s = stream::cycle(vec![6, 7, 8]);
+        let mut total = 0;
+
+        while let Some(v) = s.next().await {
+            total += v;
+            if total == 42 {
+                println!("Found {} the meaning of life!", total);
+                break;
+            }
+        }
+
+        Ok(())
+    })
+}

src/stream/cycle.rs

@@ -0,0 +1,57 @@
+use std::pin::Pin;
+use std::sync::Mutex;
+
+use crate::task::{Context, Poll};
+
+/// Creates a stream that yields the same elements continually.
+///
+/// # Examples
+///
+/// ```
+/// # #![feature(async_await)]
+/// # fn main() { 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>(items: Vec<T>) -> Cycle<T>
+where
+    T: Clone,
+{
+    Cycle {
+        items,
+        cursor: Mutex::new(0_usize),
+    }
+}
+
+/// A stream that yields the same elements continually.
+///
+/// This stream is constructed by the [`cycle`] function.
+///
+/// [`cycle`]: fn.cycle.html
+#[derive(Debug)]
+pub struct Cycle<T> {
+    items: Vec<T>,
+    cursor: Mutex<usize>,
+}
+
+impl<T: Clone> futures::Stream for Cycle<T> {
+    type Item = T;
+
+    fn poll_next(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let cursor = &mut *self.cursor.lock().unwrap();
+        let p = Poll::Ready(self.items.get(*cursor).map(|x| x.to_owned()));
+        *cursor = (*cursor + 1_usize) % self.items.len();
+        p
+    }
+}

src/stream/mod.rs

@@ -22,11 +22,13 @@
 //! # }) }
 //! ```
 
+pub use cycle::{cycle, Cycle};
 pub use empty::{empty, Empty};
 pub use once::{once, Once};
 pub use repeat::{repeat, Repeat};
 pub use stream::{Stream, Take};
 
+mod cycle;
 mod empty;
 mod once;
 mod repeat;