| use core::fmt; |
| use core::pin::Pin; |
| use futures_core::future::Future; |
| use futures_core::stream::{Stream, FusedStream}; |
| use futures_core::task::{Context, Poll}; |
| #[cfg(feature = "sink")] |
| use futures_sink::Sink; |
| use pin_project::pin_project; |
| |
| /// Stream for the [`take_while`](super::StreamExt::take_while) method. |
| #[pin_project] |
| #[must_use = "streams do nothing unless polled"] |
| pub struct TakeWhile<St: Stream, Fut, F> { |
| #[pin] |
| stream: St, |
| f: F, |
| #[pin] |
| pending_fut: Option<Fut>, |
| pending_item: Option<St::Item>, |
| done_taking: bool, |
| } |
| |
| impl<St, Fut, F> fmt::Debug for TakeWhile<St, Fut, F> |
| where |
| St: Stream + fmt::Debug, |
| St::Item: fmt::Debug, |
| Fut: fmt::Debug, |
| { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("TakeWhile") |
| .field("stream", &self.stream) |
| .field("pending_fut", &self.pending_fut) |
| .field("pending_item", &self.pending_item) |
| .field("done_taking", &self.done_taking) |
| .finish() |
| } |
| } |
| |
| impl<St, Fut, F> TakeWhile<St, Fut, F> |
| where St: Stream, |
| F: FnMut(&St::Item) -> Fut, |
| Fut: Future<Output = bool>, |
| { |
| pub(super) fn new(stream: St, f: F) -> TakeWhile<St, Fut, F> { |
| TakeWhile { |
| stream, |
| f, |
| pending_fut: None, |
| pending_item: None, |
| done_taking: false, |
| } |
| } |
| |
| delegate_access_inner!(stream, St, ()); |
| } |
| |
| impl<St, Fut, F> Stream for TakeWhile<St, Fut, F> |
| where St: Stream, |
| F: FnMut(&St::Item) -> Fut, |
| Fut: Future<Output = bool>, |
| { |
| type Item = St::Item; |
| |
| fn poll_next( |
| self: Pin<&mut Self>, |
| cx: &mut Context<'_>, |
| ) -> Poll<Option<St::Item>> { |
| if self.done_taking { |
| return Poll::Ready(None); |
| } |
| |
| let mut this = self.project(); |
| |
| Poll::Ready(loop { |
| if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() { |
| let take = ready!(fut.poll(cx)); |
| let item = this.pending_item.take(); |
| this.pending_fut.set(None); |
| if take { |
| break item; |
| } else { |
| *this.done_taking = true; |
| break None; |
| } |
| } else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) { |
| this.pending_fut.set(Some((this.f)(&item))); |
| *this.pending_item = Some(item); |
| } else { |
| break None; |
| } |
| }) |
| } |
| |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| if self.done_taking { |
| return (0, Some(0)); |
| } |
| |
| let pending_len = if self.pending_item.is_some() { 1 } else { 0 }; |
| let (_, upper) = self.stream.size_hint(); |
| let upper = match upper { |
| Some(x) => x.checked_add(pending_len), |
| None => None, |
| }; |
| (0, upper) // can't know a lower bound, due to the predicate |
| } |
| } |
| |
| impl<St, Fut, F> FusedStream for TakeWhile<St, Fut, F> |
| where St: FusedStream, |
| F: FnMut(&St::Item) -> Fut, |
| Fut: Future<Output = bool>, |
| { |
| fn is_terminated(&self) -> bool { |
| self.done_taking || self.pending_item.is_none() && self.stream.is_terminated() |
| } |
| } |
| |
| // Forwarding impl of Sink from the underlying stream |
| #[cfg(feature = "sink")] |
| impl<S, Fut, F, Item> Sink<Item> for TakeWhile<S, Fut, F> |
| where S: Stream + Sink<Item>, |
| { |
| type Error = S::Error; |
| |
| delegate_sink!(stream, Item); |
| } |