1 use crate::stream::Stream; 2 3 use core::fmt; 4 use core::pin::Pin; 5 use core::task::{Context, Poll}; 6 use pin_project_lite::pin_project; 7 8 pin_project! { 9 /// Stream returned by the [`filter`](super::StreamExt::filter) method. 10 #[must_use = "streams do nothing unless polled"] 11 pub struct Filter<St, F> { 12 #[pin] 13 stream: St, 14 f: F, 15 } 16 } 17 18 impl<St, F> fmt::Debug for Filter<St, F> 19 where 20 St: fmt::Debug, 21 { fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result22 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { 23 f.debug_struct("Filter") 24 .field("stream", &self.stream) 25 .finish() 26 } 27 } 28 29 impl<St, F> Filter<St, F> { new(stream: St, f: F) -> Self30 pub(super) fn new(stream: St, f: F) -> Self { 31 Self { stream, f } 32 } 33 } 34 35 impl<St, F> Stream for Filter<St, F> 36 where 37 St: Stream, 38 F: FnMut(&St::Item) -> bool, 39 { 40 type Item = St::Item; 41 poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St::Item>>42 fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St::Item>> { 43 loop { 44 match ready!(self.as_mut().project().stream.poll_next(cx)) { 45 Some(e) => { 46 if (self.as_mut().project().f)(&e) { 47 return Poll::Ready(Some(e)); 48 } 49 } 50 None => return Poll::Ready(None), 51 } 52 } 53 } 54 size_hint(&self) -> (usize, Option<usize>)55 fn size_hint(&self) -> (usize, Option<usize>) { 56 (0, self.stream.size_hint().1) // can't know a lower bound, due to the predicate 57 } 58 } 59