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#![deny(missing_docs)]
use core::pin::Pin;
use futures_core::ready;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{Context, Poll};
use pin_utils::unsafe_pinned;
impl<T: ?Sized> StreamExt for T where T: Stream {}
pub trait StreamExt: Stream {
fn flatten_iters(self) -> FlattenIters<Self>
where
Self::Item: IntoIterator,
Self: Sized,
{
FlattenIters::new(self)
}
}
#[must_use = "streams do nothing unless polled"]
pub struct FlattenIters<St>
where
St: Stream,
St::Item: IntoIterator,
{
stream: St,
next: Option<<St::Item as IntoIterator>::IntoIter>,
}
impl<St> Unpin for FlattenIters<St>
where
St: Stream + Unpin,
St::Item: IntoIterator,
<St::Item as IntoIterator>::IntoIter: Unpin,
{
}
impl<St> FlattenIters<St>
where
St: Stream,
St::Item: IntoIterator,
{
unsafe_pinned!(stream: St);
unsafe_pinned!(next: Option<<St::Item as IntoIterator>::IntoIter>);
}
impl<St> FlattenIters<St>
where
St: Stream,
St::Item: IntoIterator,
{
pub(crate) fn new(stream: St) -> Self {
Self { stream, next: None }
}
pub fn get_ref(&self) -> &St {
&self.stream
}
pub fn get_mut(&mut self) -> &mut St {
&mut self.stream
}
pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut St> {
self.stream()
}
pub fn into_inner(self) -> St {
self.stream
}
}
impl<St> FusedStream for FlattenIters<St>
where
St: FusedStream,
St::Item: IntoIterator,
<St::Item as IntoIterator>::IntoIter: Unpin,
{
fn is_terminated(&self) -> bool {
self.next.is_none() && self.stream.is_terminated()
}
}
impl<St> Stream for FlattenIters<St>
where
St: Stream,
St::Item: IntoIterator,
<St::Item as IntoIterator>::IntoIter: Unpin,
{
type Item = <St::Item as IntoIterator>::Item;
fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
loop {
if self.next.is_none() {
match ready!(self.as_mut().stream().poll_next(cx)) {
Some(e) => self.as_mut().next().set(Some(e.into_iter())),
None => return Poll::Ready(None),
}
}
if let Some(item) = Option::as_mut(&mut self.as_mut().next()).unwrap().next() {
return Poll::Ready(Some(item));
} else {
self.as_mut().next().set(None);
}
}
}
}
#[cfg(test)]
mod tests {
use super::StreamExt as _;
use futures::stream::{iter, StreamExt};
#[tokio::test]
async fn test_basic() {
let mut stream =
iter(vec![vec![0_usize, 1, 2], vec![3, 4], vec![], vec![5, 6, 7]]).flatten_iters();
assert_eq!(stream.next().await, Some(0));
assert_eq!(stream.next().await, Some(1));
assert_eq!(stream.next().await, Some(2));
assert_eq!(stream.next().await, Some(3));
assert_eq!(stream.next().await, Some(4));
assert_eq!(stream.next().await, Some(5));
assert_eq!(stream.next().await, Some(6));
assert_eq!(stream.next().await, Some(7));
assert_eq!(stream.next().await, None);
}
#[tokio::test]
async fn test_empty() {
let mut stream = iter(Vec::<Vec<String>>::new()).flatten_iters();
assert_eq!(stream.next().await, None);
}
}