| 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_utils::{unsafe_pinned, unsafe_unpinned}; |
| |
| struct StateFn<S, F> { |
| state: S, |
| f: F, |
| } |
| |
| /// Stream for the [`scan`](super::StreamExt::scan) method. |
| #[must_use = "streams do nothing unless polled"] |
| pub struct Scan<St: Stream, S, Fut, F> { |
| stream: St, |
| state_f: Option<StateFn<S, F>>, |
| future: Option<Fut>, |
| } |
| |
| impl<St: Unpin + Stream, S, Fut: Unpin, F> Unpin for Scan<St, S, Fut, F> {} |
| |
| 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> { |
| unsafe_pinned!(stream: St); |
| unsafe_unpinned!(state_f: Option<StateFn<S, F>>); |
| unsafe_pinned!(future: Option<Fut>); |
| |
| /// 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) -> Scan<St, S, Fut, F> { |
| Scan { |
| stream, |
| state_f: Some(StateFn { |
| state: initial_state, |
| f, |
| }), |
| future: None, |
| } |
| } |
| |
| /// Acquires a reference to the underlying stream that this combinator is |
| /// pulling from. |
| pub fn get_ref(&self) -> &St { |
| &self.stream |
| } |
| |
| /// Acquires a mutable reference to the underlying stream that this |
| /// combinator is pulling from. |
| /// |
| /// Note that care must be taken to avoid tampering with the state of the |
| /// stream which may otherwise confuse this combinator. |
| pub fn get_mut(&mut self) -> &mut St { |
| &mut self.stream |
| } |
| |
| /// Acquires a pinned mutable reference to the underlying stream that this |
| /// combinator is pulling from. |
| /// |
| /// Note that care must be taken to avoid tampering with the state of the |
| /// stream which may otherwise confuse this combinator. |
| pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut St> { |
| self.stream() |
| } |
| |
| /// Consumes this combinator, returning the underlying stream. |
| /// |
| /// Note that this may discard intermediate state of this combinator, so |
| /// care should be taken to avoid losing resources when this is called. |
| pub fn into_inner(self) -> St { |
| self.stream |
| } |
| } |
| |
| 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(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<B>> { |
| if self.is_done_taking() { |
| return Poll::Ready(None); |
| } |
| |
| if self.future.is_none() { |
| let item = match ready!(self.as_mut().stream().poll_next(cx)) { |
| Some(e) => e, |
| None => return Poll::Ready(None), |
| }; |
| let state_f = self.as_mut().state_f().as_mut().unwrap(); |
| let fut = (state_f.f)(&mut state_f.state, item); |
| self.as_mut().future().set(Some(fut)); |
| } |
| |
| let item = ready!(self.as_mut().future().as_pin_mut().unwrap().poll(cx)); |
| self.as_mut().future().set(None); |
| |
| if item.is_none() { |
| self.as_mut().state_f().take(); |
| } |
| |
| Poll::Ready(item) |
| } |
| |
| 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); |
| } |