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-rw-r--r--third_party/rust/futures-util/src/future/either.rs317
1 files changed, 317 insertions, 0 deletions
diff --git a/third_party/rust/futures-util/src/future/either.rs b/third_party/rust/futures-util/src/future/either.rs
new file mode 100644
index 0000000000..27e5064dfb
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+++ b/third_party/rust/futures-util/src/future/either.rs
@@ -0,0 +1,317 @@
+use core::pin::Pin;
+use core::task::{Context, Poll};
+use futures_core::future::{FusedFuture, Future};
+use futures_core::stream::{FusedStream, Stream};
+#[cfg(feature = "sink")]
+use futures_sink::Sink;
+
+/// Combines two different futures, streams, or sinks having the same associated types into a single type.
+///
+/// This is useful when conditionally choosing between two distinct future types:
+///
+/// ```rust
+/// use futures::future::Either;
+///
+/// # futures::executor::block_on(async {
+/// let cond = true;
+///
+/// let fut = if cond {
+/// Either::Left(async move { 12 })
+/// } else {
+/// Either::Right(async move { 44 })
+/// };
+///
+/// assert_eq!(fut.await, 12);
+/// # })
+/// ```
+#[derive(Debug, Clone)]
+pub enum Either<A, B> {
+ /// First branch of the type
+ Left(/* #[pin] */ A),
+ /// Second branch of the type
+ Right(/* #[pin] */ B),
+}
+
+impl<A, B> Either<A, B> {
+ /// Convert `Pin<&Either<A, B>>` to `Either<Pin<&A>, Pin<&B>>`,
+ /// pinned projections of the inner variants.
+ pub fn as_pin_ref(self: Pin<&Self>) -> Either<Pin<&A>, Pin<&B>> {
+ // SAFETY: We can use `new_unchecked` because the `inner` parts are
+ // guaranteed to be pinned, as they come from `self` which is pinned.
+ unsafe {
+ match *Pin::get_ref(self) {
+ Either::Left(ref inner) => Either::Left(Pin::new_unchecked(inner)),
+ Either::Right(ref inner) => Either::Right(Pin::new_unchecked(inner)),
+ }
+ }
+ }
+
+ /// Convert `Pin<&mut Either<A, B>>` to `Either<Pin<&mut A>, Pin<&mut B>>`,
+ /// pinned projections of the inner variants.
+ pub fn as_pin_mut(self: Pin<&mut Self>) -> Either<Pin<&mut A>, Pin<&mut B>> {
+ // SAFETY: `get_unchecked_mut` is fine because we don't move anything.
+ // We can use `new_unchecked` because the `inner` parts are guaranteed
+ // to be pinned, as they come from `self` which is pinned, and we never
+ // offer an unpinned `&mut A` or `&mut B` through `Pin<&mut Self>`. We
+ // also don't have an implementation of `Drop`, nor manual `Unpin`.
+ unsafe {
+ match *Pin::get_unchecked_mut(self) {
+ Either::Left(ref mut inner) => Either::Left(Pin::new_unchecked(inner)),
+ Either::Right(ref mut inner) => Either::Right(Pin::new_unchecked(inner)),
+ }
+ }
+ }
+}
+
+impl<A, B, T> Either<(T, A), (T, B)> {
+ /// Factor out a homogeneous type from an either of pairs.
+ ///
+ /// Here, the homogeneous type is the first element of the pairs.
+ pub fn factor_first(self) -> (T, Either<A, B>) {
+ match self {
+ Either::Left((x, a)) => (x, Either::Left(a)),
+ Either::Right((x, b)) => (x, Either::Right(b)),
+ }
+ }
+}
+
+impl<A, B, T> Either<(A, T), (B, T)> {
+ /// Factor out a homogeneous type from an either of pairs.
+ ///
+ /// Here, the homogeneous type is the second element of the pairs.
+ pub fn factor_second(self) -> (Either<A, B>, T) {
+ match self {
+ Either::Left((a, x)) => (Either::Left(a), x),
+ Either::Right((b, x)) => (Either::Right(b), x),
+ }
+ }
+}
+
+impl<T> Either<T, T> {
+ /// Extract the value of an either over two equivalent types.
+ pub fn into_inner(self) -> T {
+ match self {
+ Either::Left(x) => x,
+ Either::Right(x) => x,
+ }
+ }
+}
+
+impl<A, B> Future for Either<A, B>
+where
+ A: Future,
+ B: Future<Output = A::Output>,
+{
+ type Output = A::Output;
+
+ fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+ match self.as_pin_mut() {
+ Either::Left(x) => x.poll(cx),
+ Either::Right(x) => x.poll(cx),
+ }
+ }
+}
+
+impl<A, B> FusedFuture for Either<A, B>
+where
+ A: FusedFuture,
+ B: FusedFuture<Output = A::Output>,
+{
+ fn is_terminated(&self) -> bool {
+ match self {
+ Either::Left(x) => x.is_terminated(),
+ Either::Right(x) => x.is_terminated(),
+ }
+ }
+}
+
+impl<A, B> Stream for Either<A, B>
+where
+ A: Stream,
+ B: Stream<Item = A::Item>,
+{
+ type Item = A::Item;
+
+ fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+ match self.as_pin_mut() {
+ Either::Left(x) => x.poll_next(cx),
+ Either::Right(x) => x.poll_next(cx),
+ }
+ }
+
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ match self {
+ Either::Left(x) => x.size_hint(),
+ Either::Right(x) => x.size_hint(),
+ }
+ }
+}
+
+impl<A, B> FusedStream for Either<A, B>
+where
+ A: FusedStream,
+ B: FusedStream<Item = A::Item>,
+{
+ fn is_terminated(&self) -> bool {
+ match self {
+ Either::Left(x) => x.is_terminated(),
+ Either::Right(x) => x.is_terminated(),
+ }
+ }
+}
+
+#[cfg(feature = "sink")]
+impl<A, B, Item> Sink<Item> for Either<A, B>
+where
+ A: Sink<Item>,
+ B: Sink<Item, Error = A::Error>,
+{
+ type Error = A::Error;
+
+ fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+ match self.as_pin_mut() {
+ Either::Left(x) => x.poll_ready(cx),
+ Either::Right(x) => x.poll_ready(cx),
+ }
+ }
+
+ fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
+ match self.as_pin_mut() {
+ Either::Left(x) => x.start_send(item),
+ Either::Right(x) => x.start_send(item),
+ }
+ }
+
+ fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+ match self.as_pin_mut() {
+ Either::Left(x) => x.poll_flush(cx),
+ Either::Right(x) => x.poll_flush(cx),
+ }
+ }
+
+ fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+ match self.as_pin_mut() {
+ Either::Left(x) => x.poll_close(cx),
+ Either::Right(x) => x.poll_close(cx),
+ }
+ }
+}
+
+#[cfg(feature = "io")]
+#[cfg(feature = "std")]
+mod if_std {
+ use super::*;
+
+ use core::pin::Pin;
+ use core::task::{Context, Poll};
+ use futures_io::{
+ AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, IoSlice, IoSliceMut, Result, SeekFrom,
+ };
+
+ impl<A, B> AsyncRead for Either<A, B>
+ where
+ A: AsyncRead,
+ B: AsyncRead,
+ {
+ fn poll_read(
+ self: Pin<&mut Self>,
+ cx: &mut Context<'_>,
+ buf: &mut [u8],
+ ) -> Poll<Result<usize>> {
+ match self.as_pin_mut() {
+ Either::Left(x) => x.poll_read(cx, buf),
+ Either::Right(x) => x.poll_read(cx, buf),
+ }
+ }
+
+ fn poll_read_vectored(
+ self: Pin<&mut Self>,
+ cx: &mut Context<'_>,
+ bufs: &mut [IoSliceMut<'_>],
+ ) -> Poll<Result<usize>> {
+ match self.as_pin_mut() {
+ Either::Left(x) => x.poll_read_vectored(cx, bufs),
+ Either::Right(x) => x.poll_read_vectored(cx, bufs),
+ }
+ }
+ }
+
+ impl<A, B> AsyncWrite for Either<A, B>
+ where
+ A: AsyncWrite,
+ B: AsyncWrite,
+ {
+ fn poll_write(
+ self: Pin<&mut Self>,
+ cx: &mut Context<'_>,
+ buf: &[u8],
+ ) -> Poll<Result<usize>> {
+ match self.as_pin_mut() {
+ Either::Left(x) => x.poll_write(cx, buf),
+ Either::Right(x) => x.poll_write(cx, buf),
+ }
+ }
+
+ fn poll_write_vectored(
+ self: Pin<&mut Self>,
+ cx: &mut Context<'_>,
+ bufs: &[IoSlice<'_>],
+ ) -> Poll<Result<usize>> {
+ match self.as_pin_mut() {
+ Either::Left(x) => x.poll_write_vectored(cx, bufs),
+ Either::Right(x) => x.poll_write_vectored(cx, bufs),
+ }
+ }
+
+ fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>> {
+ match self.as_pin_mut() {
+ Either::Left(x) => x.poll_flush(cx),
+ Either::Right(x) => x.poll_flush(cx),
+ }
+ }
+
+ fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>> {
+ match self.as_pin_mut() {
+ Either::Left(x) => x.poll_close(cx),
+ Either::Right(x) => x.poll_close(cx),
+ }
+ }
+ }
+
+ impl<A, B> AsyncSeek for Either<A, B>
+ where
+ A: AsyncSeek,
+ B: AsyncSeek,
+ {
+ fn poll_seek(
+ self: Pin<&mut Self>,
+ cx: &mut Context<'_>,
+ pos: SeekFrom,
+ ) -> Poll<Result<u64>> {
+ match self.as_pin_mut() {
+ Either::Left(x) => x.poll_seek(cx, pos),
+ Either::Right(x) => x.poll_seek(cx, pos),
+ }
+ }
+ }
+
+ impl<A, B> AsyncBufRead for Either<A, B>
+ where
+ A: AsyncBufRead,
+ B: AsyncBufRead,
+ {
+ fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<&[u8]>> {
+ match self.as_pin_mut() {
+ Either::Left(x) => x.poll_fill_buf(cx),
+ Either::Right(x) => x.poll_fill_buf(cx),
+ }
+ }
+
+ fn consume(self: Pin<&mut Self>, amt: usize) {
+ match self.as_pin_mut() {
+ Either::Left(x) => x.consume(amt),
+ Either::Right(x) => x.consume(amt),
+ }
+ }
+ }
+}
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