| use core::fmt; |
| use core::pin::Pin; |
| use futures_core::future::Future; |
| use futures_core::stream::{FusedStream, Stream}; |
| use futures_core::task::{Context, Poll}; |
| #[cfg(feature = "sink")] |
| use futures_sink::Sink; |
| use pin_project::pin_project; |
| |
| /// Stream for the [`then`](super::StreamExt::then) method. |
| #[pin_project] |
| #[must_use = "streams do nothing unless polled"] |
| pub struct Then<St, Fut, F> { |
| #[pin] |
| stream: St, |
| #[pin] |
| future: Option<Fut>, |
| f: F, |
| } |
| |
| impl<St, Fut, F> fmt::Debug for Then<St, Fut, F> |
| where |
| St: fmt::Debug, |
| Fut: fmt::Debug, |
| { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("Then") |
| .field("stream", &self.stream) |
| .field("future", &self.future) |
| .finish() |
| } |
| } |
| |
| impl<St, Fut, F> Then<St, Fut, F> |
| where St: Stream, |
| F: FnMut(St::Item) -> Fut, |
| { |
| pub(super) fn new(stream: St, f: F) -> Then<St, Fut, F> { |
| Then { |
| stream, |
| future: None, |
| f, |
| } |
| } |
| |
| delegate_access_inner!(stream, St, ()); |
| } |
| |
| impl<St, Fut, F> FusedStream for Then<St, Fut, F> |
| where St: FusedStream, |
| F: FnMut(St::Item) -> Fut, |
| Fut: Future, |
| { |
| fn is_terminated(&self) -> bool { |
| self.future.is_none() && self.stream.is_terminated() |
| } |
| } |
| |
| impl<St, Fut, F> Stream for Then<St, Fut, F> |
| where St: Stream, |
| F: FnMut(St::Item) -> Fut, |
| Fut: Future, |
| { |
| type Item = Fut::Output; |
| |
| fn poll_next( |
| self: Pin<&mut Self>, |
| cx: &mut Context<'_>, |
| ) -> Poll<Option<Self::Item>> { |
| 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); |
| break Some(item); |
| } else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) { |
| this.future.set(Some((this.f)(item))); |
| } else { |
| break None; |
| } |
| }) |
| } |
| |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| let future_len = if self.future.is_some() { 1 } else { 0 }; |
| let (lower, upper) = self.stream.size_hint(); |
| let lower = lower.saturating_add(future_len); |
| let upper = match upper { |
| Some(x) => x.checked_add(future_len), |
| None => None, |
| }; |
| (lower, upper) |
| } |
| } |
| |
| // Forwarding impl of Sink from the underlying stream |
| #[cfg(feature = "sink")] |
| impl<S, Fut, F, Item> Sink<Item> for Then<S, Fut, F> |
| where S: Sink<Item>, |
| { |
| type Error = S::Error; |
| |
| delegate_sink!(stream, Item); |
| } |