1 use core::pin::Pin; 2 use futures_core::ready; 3 use futures_core::stream::{FusedStream, Stream}; 4 use futures_core::task::{Context, Poll}; 5 #[cfg(feature = "sink")] 6 use futures_sink::Sink; 7 use pin_project_lite::pin_project; 8 9 pin_project! { 10 /// Stream for the [`enumerate`](super::StreamExt::enumerate) method. 11 #[derive(Debug)] 12 #[must_use = "streams do nothing unless polled"] 13 pub struct Enumerate<St> { 14 #[pin] 15 stream: St, 16 count: usize, 17 } 18 } 19 20 impl<St: Stream> Enumerate<St> { new(stream: St) -> Self21 pub(super) fn new(stream: St) -> Self { 22 Self { stream, count: 0 } 23 } 24 25 delegate_access_inner!(stream, St, ()); 26 } 27 28 impl<St: Stream + FusedStream> FusedStream for Enumerate<St> { is_terminated(&self) -> bool29 fn is_terminated(&self) -> bool { 30 self.stream.is_terminated() 31 } 32 } 33 34 impl<St: Stream> Stream for Enumerate<St> { 35 type Item = (usize, St::Item); 36 poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>>37 fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> { 38 let this = self.project(); 39 40 match ready!(this.stream.poll_next(cx)) { 41 Some(item) => { 42 let prev_count = *this.count; 43 *this.count += 1; 44 Poll::Ready(Some((prev_count, item))) 45 } 46 None => Poll::Ready(None), 47 } 48 } 49 size_hint(&self) -> (usize, Option<usize>)50 fn size_hint(&self) -> (usize, Option<usize>) { 51 self.stream.size_hint() 52 } 53 } 54 55 // Forwarding impl of Sink from the underlying stream 56 #[cfg(feature = "sink")] 57 impl<S, Item> Sink<Item> for Enumerate<S> 58 where 59 S: Stream + Sink<Item>, 60 { 61 type Error = S::Error; 62 63 delegate_sink!(stream, Item); 64 } 65