| use crate::stream_ext::Fuse; |
| use crate::Stream; |
| |
| use core::pin::Pin; |
| use core::task::{Context, Poll}; |
| use pin_project_lite::pin_project; |
| |
| pin_project! { |
| /// Stream returned by the [`merge`](super::StreamExt::merge) method. |
| pub struct Merge<T, U> { |
| #[pin] |
| a: Fuse<T>, |
| #[pin] |
| b: Fuse<U>, |
| // When `true`, poll `a` first, otherwise, `poll` b`. |
| a_first: bool, |
| } |
| } |
| |
| impl<T, U> Merge<T, U> { |
| pub(super) fn new(a: T, b: U) -> Merge<T, U> |
| where |
| T: Stream, |
| U: Stream, |
| { |
| Merge { |
| a: Fuse::new(a), |
| b: Fuse::new(b), |
| a_first: true, |
| } |
| } |
| } |
| |
| impl<T, U> Stream for Merge<T, U> |
| where |
| T: Stream, |
| U: Stream<Item = T::Item>, |
| { |
| type Item = T::Item; |
| |
| fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T::Item>> { |
| let me = self.project(); |
| let a_first = *me.a_first; |
| |
| // Toggle the flag |
| *me.a_first = !a_first; |
| |
| if a_first { |
| poll_next(me.a, me.b, cx) |
| } else { |
| poll_next(me.b, me.a, cx) |
| } |
| } |
| |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| super::merge_size_hints(self.a.size_hint(), self.b.size_hint()) |
| } |
| } |
| |
| fn poll_next<T, U>( |
| first: Pin<&mut T>, |
| second: Pin<&mut U>, |
| cx: &mut Context<'_>, |
| ) -> Poll<Option<T::Item>> |
| where |
| T: Stream, |
| U: Stream<Item = T::Item>, |
| { |
| use Poll::*; |
| |
| let mut done = true; |
| |
| match first.poll_next(cx) { |
| Ready(Some(val)) => return Ready(Some(val)), |
| Ready(None) => {} |
| Pending => done = false, |
| } |
| |
| match second.poll_next(cx) { |
| Ready(Some(val)) => return Ready(Some(val)), |
| Ready(None) => {} |
| Pending => done = false, |
| } |
| |
| if done { |
| Ready(None) |
| } else { |
| Pending |
| } |
| } |