1 use core::pin::Pin; 2 use core::usize; 3 use futures_core::ready; 4 use futures_core::stream::{FusedStream, Stream}; 5 use futures_core::task::{Context, Poll}; 6 use pin_project_lite::pin_project; 7 8 pin_project! { 9 /// Stream for the [`cycle`](super::StreamExt::cycle) method. 10 #[derive(Debug)] 11 #[must_use = "streams do nothing unless polled"] 12 pub struct Cycle<St> { 13 orig: St, 14 #[pin] 15 stream: St, 16 } 17 } 18 19 impl<St> Cycle<St> 20 where 21 St: Clone + Stream, 22 { new(stream: St) -> Self23 pub(super) fn new(stream: St) -> Self { 24 Self { orig: stream.clone(), stream } 25 } 26 } 27 28 impl<St> Stream for Cycle<St> 29 where 30 St: Clone + Stream, 31 { 32 type Item = St::Item; 33 poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>>34 fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> { 35 let mut this = self.project(); 36 37 match ready!(this.stream.as_mut().poll_next(cx)) { 38 None => { 39 this.stream.set(this.orig.clone()); 40 this.stream.poll_next(cx) 41 } 42 item => Poll::Ready(item), 43 } 44 } 45 size_hint(&self) -> (usize, Option<usize>)46 fn size_hint(&self) -> (usize, Option<usize>) { 47 // the cycle stream is either empty or infinite 48 match self.orig.size_hint() { 49 size @ (0, Some(0)) => size, 50 (0, _) => (0, None), 51 _ => (usize::max_value(), None), 52 } 53 } 54 } 55 56 impl<St> FusedStream for Cycle<St> 57 where 58 St: Clone + Stream, 59 { is_terminated(&self) -> bool60 fn is_terminated(&self) -> bool { 61 // the cycle stream is either empty or infinite 62 if let (0, Some(0)) = self.size_hint() { 63 true 64 } else { 65 false 66 } 67 } 68 } 69