Add TryAny adapter

futures-util/src/stream/try_stream/mod.rs

@@ -168,6 +168,10 @@ mod try_all;
 #[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
 pub use self::try_all::TryAll;
 
+mod try_any;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::try_any::TryAny;
+
 impl<S: ?Sized + TryStream> TryStreamExt for S {}
 
 /// Adapters specific to `Result`-returning streams
@@ -1104,4 +1108,33 @@ pub trait TryStreamExt: TryStream {
     {
         assert_future::<Result<bool, Self::Error>, _>(TryAll::new(self, f))
     }
+
+    /// Attempt to execute a predicate over an asynchronous stream and evaluate if any items
+    /// satisfy the predicate. Exits early if an `Err` is encountered or if an `Ok` item is found
+    /// that satisfies the predicate.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # futures::executor::block_on(async {
+    /// use futures::stream::{self, StreamExt, TryStreamExt};
+    /// use std::convert::Infallible;
+    ///
+    /// let number_stream = stream::iter(0..10).map(Ok::<_, Infallible>);
+    /// let contain_three = number_stream.try_any(|i| async move { i == 3 });
+    /// assert_eq!(contain_three.await, Ok(true));
+    ///
+    /// let stream_with_errors = stream::iter([Ok(1), Err("err"), Ok(3)]);
+    /// let contain_three = stream_with_errors.try_any(|i| async move { i == 3 });
+    /// assert_eq!(contain_three.await, Err("err"));
+    /// # });
+    /// ```
+    fn try_any<Fut, F>(self, f: F) -> TryAny<Self, Fut, F>
+    where
+        Self: Sized,
+        F: FnMut(Self::Ok) -> Fut,
+        Fut: Future<Output = bool>,
+    {
+        assert_future::<Result<bool, Self::Error>, _>(TryAny::new(self, f))
+    }
 }

futures-util/src/stream/try_stream/try_any.rs

@@ -0,0 +1,98 @@
+use core::fmt;
+use core::pin::Pin;
+use futures_core::future::{FusedFuture, Future};
+use futures_core::ready;
+use futures_core::stream::TryStream;
+use futures_core::task::{Context, Poll};
+use pin_project_lite::pin_project;
+
+pin_project! {
+    /// Future for the [`any`](super::StreamExt::any) method.
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct TryAny<St, Fut, F> {
+        #[pin]
+        stream: St,
+        f: F,
+        done: bool,
+        #[pin]
+        future: Option<Fut>,
+    }
+}
+
+impl<St, Fut, F> fmt::Debug for TryAny<St, Fut, F>
+where
+    St: fmt::Debug,
+    Fut: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("TryAny")
+            .field("stream", &self.stream)
+            .field("done", &self.done)
+            .field("future", &self.future)
+            .finish()
+    }
+}
+
+impl<St, Fut, F> TryAny<St, Fut, F>
+where
+    St: TryStream,
+    F: FnMut(St::Ok) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    pub(super) fn new(stream: St, f: F) -> Self {
+        Self { stream, f, done: false, future: None }
+    }
+}
+
+impl<St, Fut, F> FusedFuture for TryAny<St, Fut, F>
+where
+    St: TryStream,
+    F: FnMut(St::Ok) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    fn is_terminated(&self) -> bool {
+        self.done && self.future.is_none()
+    }
+}
+
+impl<St, Fut, F> Future for TryAny<St, Fut, F>
+where
+    St: TryStream,
+    F: FnMut(St::Ok) -> Fut,
+    Fut: Future<Output = bool>,
+{
+    type Output = Result<bool, St::Error>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<bool, St::Error>> {
+        let mut this = self.project();
+
+        Poll::Ready(loop {
+            if let Some(fut) = this.future.as_mut().as_pin_mut() {
+                // we're currently processing a future to produce a new value
+                let acc = ready!(fut.poll(cx));
+                this.future.set(None);
+                if acc {
+                    *this.done = true;
+                    break Ok(true);
+                } // early exit
+            } else if !*this.done {
+                // we're waiting on a new item from the stream
+                match ready!(this.stream.as_mut().try_poll_next(cx)) {
+                    Some(Ok(item)) => {
+                        this.future.set(Some((this.f)(item)));
+                    }
+                    Some(Err(err)) => {
+                        *this.done = true;
+                        break Err(err);
+                    }
+                    None => {
+                        *this.done = true;
+                        break Ok(false);
+                    }
+                }
+            } else {
+                panic!("TryAny polled after completion")
+            }
+        })
+    }
+}

futures/tests/stream_try_stream.rs

@@ -159,3 +159,25 @@ fn try_all() {
         assert_eq!(Err("err"), all);
     });
 }
+
+#[test]
+fn try_any() {
+    block_on(async {
+        let empty: [Result<u8, Infallible>; 0] = [];
+        let st = stream::iter(empty);
+        let any = st.try_any(is_even).await;
+        assert_eq!(Ok(false), any);
+
+        let st = stream::iter([Ok::<_, Infallible>(1), Ok(2), Ok(3)]);
+        let any = st.try_any(is_even).await;
+        assert_eq!(Ok(true), any);
+
+        let st = stream::iter([Ok::<_, Infallible>(1), Ok(3), Ok(5)]);
+        let any = st.try_any(is_even).await;
+        assert_eq!(Ok(false), any);
+
+        let st = stream::iter([Ok(1), Ok(3), Err("err"), Ok(8)]);
+        let any = st.try_any(is_even).await;
+        assert_eq!(Err("err"), any);
+    });
+}