diff options
Diffstat (limited to 'src/stream_ext/map_while.rs')
-rw-r--r-- | src/stream_ext/map_while.rs | 52 |
1 files changed, 52 insertions, 0 deletions
diff --git a/src/stream_ext/map_while.rs b/src/stream_ext/map_while.rs new file mode 100644 index 0000000..d4fd825 --- /dev/null +++ b/src/stream_ext/map_while.rs @@ -0,0 +1,52 @@ +use crate::Stream; + +use core::fmt; +use core::pin::Pin; +use core::task::{Context, Poll}; +use pin_project_lite::pin_project; + +pin_project! { + /// Stream for the [`map_while`](super::StreamExt::map_while) method. + #[must_use = "streams do nothing unless polled"] + pub struct MapWhile<St, F> { + #[pin] + stream: St, + f: F, + } +} + +impl<St, F> fmt::Debug for MapWhile<St, F> +where + St: fmt::Debug, +{ + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_struct("MapWhile") + .field("stream", &self.stream) + .finish() + } +} + +impl<St, F> MapWhile<St, F> { + pub(super) fn new(stream: St, f: F) -> Self { + MapWhile { stream, f } + } +} + +impl<St, F, T> Stream for MapWhile<St, F> +where + St: Stream, + F: FnMut(St::Item) -> Option<T>, +{ + type Item = T; + + fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> { + let me = self.project(); + let f = me.f; + me.stream.poll_next(cx).map(|opt| opt.and_then(f)) + } + + fn size_hint(&self) -> (usize, Option<usize>) { + let (_, upper) = self.stream.size_hint(); + (0, upper) + } +} |