Add Future/Stream bounds to FusedFuture/FusedStream

Author: taiki-e

futures-core/src/future/mod.rs

@@ -18,20 +18,20 @@ pub type BoxFuture<'a, T> = Pin<alloc::boxed::Box<dyn Future<Output = T> + Send
 #[cfg(feature = "alloc")]
 pub type LocalBoxFuture<'a, T> = Pin<alloc::boxed::Box<dyn Future<Output = T> + 'a>>;
 
-/// A `Future` or `TryFuture` which tracks whether or not the underlying future
+/// A future which tracks whether or not the underlying future
 /// should no longer be polled.
 ///
 /// `is_terminated` will return `true` if a future should no longer be polled.
 /// Usually, this state occurs after `poll` (or `try_poll`) returned
 /// `Poll::Ready`. However, `is_terminated` may also return `true` if a future
 /// has become inactive and can no longer make progress and should be ignored
 /// or dropped rather than being `poll`ed again.
-pub trait FusedFuture {
+pub trait FusedFuture: Future {
     /// Returns `true` if the underlying future should no longer be polled.
     fn is_terminated(&self) -> bool;
 }
 
-impl<F: FusedFuture + ?Sized> FusedFuture for &mut F {
+impl<F: FusedFuture + ?Sized + Unpin> FusedFuture for &mut F {
     fn is_terminated(&self) -> bool {
         <F as FusedFuture>::is_terminated(&**self)
     }
@@ -92,7 +92,7 @@ mod if_alloc {
     use alloc::boxed::Box;
     use super::*;
 
-    impl<F: FusedFuture + ?Sized> FusedFuture for Box<F> {
+    impl<F: FusedFuture + ?Sized + Unpin> FusedFuture for Box<F> {
         fn is_terminated(&self) -> bool {
             <F as FusedFuture>::is_terminated(&**self)
         }

futures-core/src/stream.rs

@@ -87,20 +87,20 @@ where
     }
 }
 
-/// A `Stream` or `TryStream` which tracks whether or not the underlying stream
+/// A stream which tracks whether or not the underlying stream
 /// should no longer be polled.
 ///
 /// `is_terminated` will return `true` if a future should no longer be polled.
 /// Usually, this state occurs after `poll_next` (or `try_poll_next`) returned
 /// `Poll::Ready(None)`. However, `is_terminated` may also return `true` if a
 /// stream has become inactive and can no longer make progress and should be
 /// ignored or dropped rather than being polled again.
-pub trait FusedStream {
+pub trait FusedStream: Stream {
     /// Returns `true` if the stream should no longer be polled.
     fn is_terminated(&self) -> bool;
 }
 
-impl<F: ?Sized + FusedStream> FusedStream for &mut F {
+impl<F: ?Sized + FusedStream + Unpin> FusedStream for &mut F {
     fn is_terminated(&self) -> bool {
         <F as FusedStream>::is_terminated(&**self)
     }
@@ -194,7 +194,7 @@ mod if_alloc {
         }
     }
 
-    impl<S: ?Sized + FusedStream> FusedStream for Box<S> {
+    impl<S: ?Sized + FusedStream + Unpin> FusedStream for Box<S> {
         fn is_terminated(&self) -> bool {
             <S as FusedStream>::is_terminated(&**self)
         }

futures-util/src/future/either.rs

@@ -69,7 +69,7 @@ where
 impl<A, B> FusedFuture for Either<A, B>
 where
     A: FusedFuture,
-    B: FusedFuture,
+    B: FusedFuture<Output = A::Output>,
 {
     fn is_terminated(&self) -> bool {
         match self {
@@ -99,7 +99,7 @@ where
 impl<A, B> FusedStream for Either<A, B>
 where
     A: FusedStream,
-    B: FusedStream,
+    B: FusedStream<Item = A::Item>,
 {
     fn is_terminated(&self) -> bool {
         match self {

futures-util/src/future/inspect.rs

@@ -25,7 +25,10 @@ impl<Fut: Future, F: FnOnce(&Fut::Output)> Inspect<Fut, F> {
 
 impl<Fut: Future + Unpin, F> Unpin for Inspect<Fut, F> {}
 
-impl<Fut: Future + FusedFuture, F> FusedFuture for Inspect<Fut, F> {
+impl<Fut, F> FusedFuture for Inspect<Fut, F>
+    where Fut: FusedFuture,
+          F: FnOnce(&Fut::Output),
+{
     fn is_terminated(&self) -> bool { self.future.is_terminated() }
 }
 

futures-util/src/future/lazy.rs

@@ -38,11 +38,13 @@ pub fn lazy<F, R>(f: F) -> Lazy<F>
     Lazy { f: Some(f) }
 }
 
-impl<F> FusedFuture for Lazy<F> {
+impl<F, R> FusedFuture for Lazy<F>
+    where F: FnOnce(&mut Context<'_>) -> R,
+{
     fn is_terminated(&self) -> bool { self.f.is_none() }
 }
 
-impl<R, F> Future for Lazy<F>
+impl<F, R> Future for Lazy<F>
     where F: FnOnce(&mut Context<'_>) -> R,
 {
     type Output = R;

futures-util/src/future/map.rs

@@ -23,7 +23,10 @@ impl<Fut, F> Map<Fut, F> {
 
 impl<Fut: Unpin, F> Unpin for Map<Fut, F> {}
 
-impl<Fut, F> FusedFuture for Map<Fut, F> {
+impl<Fut, F, T> FusedFuture for Map<Fut, F>
+    where Fut: Future,
+          F: FnOnce(Fut::Output) -> T,
+{
     fn is_terminated(&self) -> bool { self.f.is_none() }
 }
 

futures-util/src/future/shared.rs

@@ -173,14 +173,19 @@ where
     }
 }
 
-impl<Fut: Future> FusedFuture for Shared<Fut> {
+impl<Fut> FusedFuture for Shared<Fut>
+where
+    Fut: Future,
+    Fut::Output: Clone,
+{
     fn is_terminated(&self) -> bool {
         self.inner.is_none()
     }
 }
 
-impl<Fut: Future> Future for Shared<Fut>
+impl<Fut> Future for Shared<Fut>
 where
+    Fut: Future,
     Fut::Output: Clone,
 {
     type Output = Fut::Output;

futures-util/src/future/then.rs

@@ -25,7 +25,11 @@ impl<Fut1, Fut2, F> Then<Fut1, Fut2, F>
     }
 }
 
-impl<Fut1, Fut2, F> FusedFuture for Then<Fut1, Fut2, F> {
+impl<Fut1, Fut2, F> FusedFuture for Then<Fut1, Fut2, F>
+    where Fut1: Future,
+          Fut2: Future,
+          F: FnOnce(Fut1::Output) -> Fut2,
+{
     fn is_terminated(&self) -> bool { self.chain.is_terminated() }
 }
 

futures-util/src/stream/chain.rs

@@ -27,7 +27,10 @@ where St1: Stream,
     }
 }
 
-impl<St1, St2: FusedStream> FusedStream for Chain<St1, St2> {
+impl<St1, St2> FusedStream for Chain<St1, St2>
+where St1: Stream,
+      St2: FusedStream<Item=St1::Item>,
+{
     fn is_terminated(&self) -> bool {
         self.first.is_none() && self.second.is_terminated()
     }

futures-util/src/stream/collect.rs

@@ -31,7 +31,10 @@ impl<St: Stream, C: Default> Collect<St, C> {
     }
 }
 
-impl<St: FusedStream, C> FusedFuture for Collect<St, C> {
+impl<St, C> FusedFuture for Collect<St, C>
+where St: FusedStream,
+      C: Default + Extend<St:: Item>
+{
     fn is_terminated(&self) -> bool {
         self.stream.is_terminated()
     }