Add stream::next implementation

Author: Roman Proskuryakov

src/lib.rs

@@ -1,3 +1,4 @@
 #![feature(async_await, await_macro, futures_api)]
 
 pub mod future;
+pub mod stream;

src/stream.rs

@@ -0,0 +1,29 @@
+use futures::stream::Stream;
+use core::pin::Pin;
+
+pub async fn next<St>(stream: &mut St) -> Option<St::Item>
+    where St: Stream + Unpin,
+{
+    use futures::future::poll_fn;
+    use futures::task::Waker;
+    let poll_next = |waker: &Waker| Pin::new(&mut *stream).poll_next(waker);
+    let future_next = poll_fn(poll_next);
+    await!(future_next)
+}
+
+#[cfg(test)]
+mod tests {
+    use futures::{stream, executor};
+    use crate::stream::*;
+
+    #[test]
+    fn test_next() {
+        let mut stream = stream::iter(1..=3);
+
+        assert_eq!(executor::block_on(next(&mut stream)), Some(1));
+        assert_eq!(executor::block_on(next(&mut stream)), Some(2));
+        assert_eq!(executor::block_on(next(&mut stream)), Some(3));
+        assert_eq!(executor::block_on(next(&mut stream)), None);
+    }
+
+}