| use core::fmt; |
| use core::pin::Pin; |
| use futures_core::future::Future; |
| use futures_core::ready; |
| use futures_core::stream::{FusedStream, Stream}; |
| use futures_core::task::{Context, Poll}; |
| #[cfg(feature = "sink")] |
| use futures_sink::Sink; |
| use pin_project_lite::pin_project; |
| |
| struct StateFn<S, F> { |
| state: S, |
| f: F, |
| } |
| |
| pin_project! { |
| /// Stream for the [`scan`](super::StreamExt::scan) method. |
| #[must_use = "streams do nothing unless polled"] |
| pub struct Scan<St: Stream, S, Fut, F> { |
| #[pin] |
| stream: St, |
| state_f: Option<StateFn<S, F>>, |
| #[pin] |
| future: Option<Fut>, |
| } |
| } |
| |
| impl<St, S, Fut, F> fmt::Debug for Scan<St, S, Fut, F> |
| where |
| St: Stream + fmt::Debug, |
| St::Item: fmt::Debug, |
| S: fmt::Debug, |
| Fut: fmt::Debug, |
| { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("Scan") |
| .field("stream", &self.stream) |
| .field("state", &self.state_f.as_ref().map(|s| &s.state)) |
| .field("future", &self.future) |
| .field("done_taking", &self.is_done_taking()) |
| .finish() |
| } |
| } |
| |
| impl<St: Stream, S, Fut, F> Scan<St, S, Fut, F> { |
| /// Checks if internal state is `None`. |
| fn is_done_taking(&self) -> bool { |
| self.state_f.is_none() |
| } |
| } |
| |
| impl<B, St, S, Fut, F> Scan<St, S, Fut, F> |
| where |
| St: Stream, |
| F: FnMut(&mut S, St::Item) -> Fut, |
| Fut: Future<Output = Option<B>>, |
| { |
| pub(super) fn new(stream: St, initial_state: S, f: F) -> Self { |
| Self { stream, state_f: Some(StateFn { state: initial_state, f }), future: None } |
| } |
| |
| delegate_access_inner!(stream, St, ()); |
| } |
| |
| impl<B, St, S, Fut, F> Stream for Scan<St, S, Fut, F> |
| where |
| St: Stream, |
| F: FnMut(&mut S, St::Item) -> Fut, |
| Fut: Future<Output = Option<B>>, |
| { |
| type Item = B; |
| |
| fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<B>> { |
| if self.is_done_taking() { |
| return Poll::Ready(None); |
| } |
| |
| let mut this = self.project(); |
| |
| Poll::Ready(loop { |
| if let Some(fut) = this.future.as_mut().as_pin_mut() { |
| let item = ready!(fut.poll(cx)); |
| this.future.set(None); |
| |
| if item.is_none() { |
| *this.state_f = None; |
| } |
| |
| break item; |
| } else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) { |
| let state_f = this.state_f.as_mut().unwrap(); |
| this.future.set(Some((state_f.f)(&mut state_f.state, item))) |
| } else { |
| break None; |
| } |
| }) |
| } |
| |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| if self.is_done_taking() { |
| (0, Some(0)) |
| } else { |
| self.stream.size_hint() // can't know a lower bound, due to the predicate |
| } |
| } |
| } |
| |
| impl<B, St, S, Fut, F> FusedStream for Scan<St, S, Fut, F> |
| where |
| St: FusedStream, |
| F: FnMut(&mut S, St::Item) -> Fut, |
| Fut: Future<Output = Option<B>>, |
| { |
| fn is_terminated(&self) -> bool { |
| self.is_done_taking() || self.future.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 Scan<S, S, Fut, F> |
| where |
| S: Stream + Sink<Item>, |
| { |
| type Error = S::Error; |
| |
| delegate_sink!(stream, Item); |
| } |