silence must use

src/stream/interval.rs

@@ -72,7 +72,7 @@ impl Stream for Interval {
             return Poll::Pending;
         }
         let interval = self.interval;
-        std::mem::replace(&mut self.delay, Timer::after(interval));
+        let _ = std::mem::replace(&mut self.delay, Timer::after(interval));
         Poll::Ready(Some(()))
     }
 }

src/stream/stream/throttle.rs

@@ -59,7 +59,7 @@ impl<S: Stream> Stream for Throttle<S> {
             Poll::Ready(None) => Poll::Ready(None),
             Poll::Ready(Some(v)) => {
                 *this.blocked = true;
-                std::mem::replace(&mut *this.delay, Timer::after(*this.duration));
+                let _ = std::mem::replace(&mut *this.delay, Timer::after(*this.duration));
                 Poll::Ready(Some(v))
             }
         }