Apply suggestions from code review

Co-authored-by: nasa <htilcs1115@gmail.com>

src/stream/stream/flat_map.rs

@@ -51,21 +51,15 @@ where
         let mut this = self.project();
         loop {
             if let Some(inner) = this.inner_stream.as_mut().as_pin_mut() {
-                let next_item = futures_core::ready!(inner.poll_next(cx));
-
-                if next_item.is_some() {
-                    return Poll::Ready(next_item);
-                } else {
-                    this.inner_stream.set(None);
+                match futures_core::ready!(inner.poll_next(cx)) {
+                    item @ Some(_) => return Poll::Ready(item),
+                    None => this.inner_stream.set(None),
                 }
             }
 
-            let inner = futures_core::ready!(this.stream.as_mut().poll_next(cx));
-
-            if inner.is_some() {
-                this.inner_stream.set(inner.map(IntoStream::into_stream));
-            } else {
-                return Poll::Ready(None);
+            match futures_core::ready!(this.stream.as_mut().poll_next(cx)) {
+                inner @ Some(_) => this.inner_stream.set(inner.map(IntoStream::into_stream)),
+                None => return Poll::Ready(None),
             }
         }
     }

src/stream/stream/flatten.rs

@@ -52,21 +52,15 @@ where
         let mut this = self.project();
         loop {
             if let Some(inner) = this.inner_stream.as_mut().as_pin_mut() {
-                let next_item = futures_core::ready!(inner.poll_next(cx));
-
-                if next_item.is_some() {
-                    return Poll::Ready(next_item);
-                } else {
-                    this.inner_stream.set(None);
+                match futures_core::ready!(inner.poll_next(cx)) {
+                    item @ Some(_) => return Poll::Ready(next_item),
+                    None => this.inner_stream.set(None),
                 }
             }
 
-            let inner = futures_core::ready!(this.stream.as_mut().poll_next(cx));
-
-            if inner.is_some() {
-                this.inner_stream.set(inner.map(IntoStream::into_stream));
-            } else {
-                return Poll::Ready(None);
+            match futures_core::ready!(this.stream.as_mut().poll_next(cx)) {
+                inner @ Some(_) => this.inner_stream.set(inner.map(IntoStream::into_stream)),
+                None => Poll::Ready(None),
             }
         }
     }