Use impl Trait syntax instead of Trait Objects.

Rust v1.26 introduced impl Trait which avoid the heap allocation with Box
and makes the code a bit more ergonomic.

For more see https://blog.rust-lang.org/2018/05/10/Rust-1.26.html

hammond-data/src/feed.rs

@@ -25,23 +25,21 @@ pub struct Feed {
 
 impl Feed {
     /// Index the contents of the RSS `Feed` into the database.
-    pub fn index(self) -> Box<Future<Item = (), Error = DataError> + Send> {
-        let fut = self.parse_podcast_async()
+    pub fn index(self) -> impl Future<Item = (), Error = DataError> + Send {
+        self.parse_podcast_async()
             .and_then(|pd| pd.to_podcast())
-            .and_then(move |pd| self.index_channel_items(pd));
-
-        Box::new(fut)
+            .and_then(move |pd| self.index_channel_items(pd))
     }
 
     fn parse_podcast(&self) -> NewPodcast {
         NewPodcast::new(&self.channel, self.source_id)
     }
 
-    fn parse_podcast_async(&self) -> Box<Future<Item = NewPodcast, Error = DataError> + Send> {
-        Box::new(ok(self.parse_podcast()))
+    fn parse_podcast_async(&self) -> impl Future<Item = NewPodcast, Error = DataError> + Send {
+        ok(self.parse_podcast())
     }
 
-    fn index_channel_items(self, pd: Podcast) -> Box<Future<Item = (), Error = DataError> + Send> {
+    fn index_channel_items(self, pd: Podcast) -> impl Future<Item = (), Error = DataError> + Send {
         let stream = stream::iter_ok::<_, DataError>(self.channel.into_items());
 
         // Parse the episodes
@@ -52,11 +50,9 @@ impl Feed {
         });
 
         // Filter errors, Index updatable episodes, return insertables.
-        let insertables = filter_episodes(episodes);
-        // Batch index insertable episodes.
-        let idx = insertables.and_then(|eps| ok(batch_insert_episodes(&eps)));
-
-        Box::new(idx)
+        filter_episodes(episodes)
+            // Batch index insertable episodes.
+            .and_then(|eps| ok(batch_insert_episodes(&eps)))
     }
 }
 
@@ -87,11 +83,11 @@ fn determine_ep_state(
 
 fn filter_episodes<'a, S>(
     stream: S,
-) -> Box<Future<Item = Vec<NewEpisode>, Error = DataError> + Send + 'a>
+) -> impl Future<Item = Vec<NewEpisode>, Error = DataError> + Send + 'a
 where
     S: Stream<Item = IndexState<NewEpisode>, Error = DataError> + Send + 'a,
 {
-    let list = stream.filter_map(|state| match state {
+    stream.filter_map(|state| match state {
         IndexState::NotChanged => None,
         // Update individual rows, and filter them
         IndexState::Update((ref ep, rowid)) => {
@@ -105,9 +101,7 @@ where
         IndexState::Index(s) => Some(s),
     })
     // only Index is left, collect them for batch index
-    .collect();
-
-    Box::new(list)
+    .collect()
 }
 
 fn batch_insert_episodes(episodes: &[NewEpisode]) {

hammond-data/src/models/source.rs

@@ -177,7 +177,7 @@ impl Source {
         self,
         client: Client<HttpsConnector<HttpConnector>>,
         ignore_etags: bool,
-    ) -> Box<Future<Item = Feed, Error = DataError>> {
+    ) -> impl Future<Item = Feed, Error = DataError> {
         let id = self.id();
         let response = loop_fn(self, move |source| {
             source
@@ -194,7 +194,7 @@ impl Source {
                 })
         });
 
-        let feed = response
+        response
             .and_then(response_to_channel)
             .and_then(move |chan| {
                 FeedBuilder::default()
@@ -202,9 +202,7 @@ impl Source {
                     .source_id(id)
                     .build()
                     .map_err(From::from)
-            });
-
-        Box::new(feed)
+            })
     }
 
     // TODO: make ignore_etags an Enum for better ergonomics.
@@ -213,7 +211,7 @@ impl Source {
         self,
         client: &Client<HttpsConnector<HttpConnector>>,
         ignore_etags: bool,
-    ) -> Box<Future<Item = Response, Error = DataError>> {
+    ) -> impl Future<Item = Response, Error = DataError> {
         // FIXME: remove unwrap somehow
         let uri = Uri::from_str(self.uri()).unwrap();
         let mut req = Request::new(Method::Get, uri);
@@ -234,25 +232,22 @@ impl Source {
             }
         }
 
-        let work = client
+        client
             .request(req)
             .map_err(From::from)
-            .and_then(move |res| self.match_status(res));
-        Box::new(work)
+            .and_then(move |res| self.match_status(res))
     }
 }
 
 #[allow(needless_pass_by_value)]
-fn response_to_channel(res: Response) -> Box<Future<Item = Channel, Error = DataError> + Send> {
-    let chan = res.body()
+fn response_to_channel(res: Response) -> impl Future<Item = Channel, Error = DataError> + Send {
+    res.body()
         .concat2()
         .map(|x| x.into_iter())
         .map_err(From::from)
         .map(|iter| iter.collect::<Vec<u8>>())
         .map(|utf_8_bytes| String::from_utf8_lossy(&utf_8_bytes).into_owned())
-        .and_then(|buf| Channel::from_str(&buf).map_err(From::from));
-
-    Box::new(chan)
+        .and_then(|buf| Channel::from_str(&buf).map_err(From::from))
 }
 
 #[cfg(test)]

hammond-data/src/pipeline.rs

@@ -50,24 +50,22 @@ pub fn pipeline<'a, S>(
     sources: S,
     ignore_etags: bool,
     client: &HttpsClient,
-) -> Box<Future<Item = Vec<()>, Error = DataError> + 'a>
+) -> impl Future<Item = Vec<()>, Error = DataError> + 'a
 where
     S: Stream<Item = Source, Error = DataError> + 'a,
 {
-    let pipeline = sources
+    sources
         .and_then(clone!(client => move |s| s.into_feed(client.clone(), ignore_etags)))
         .and_then(|feed| rayon::scope(|s| s.spawn_future(feed.index())))
         // the stream will stop at the first error so
         // we ensure that everything will succeded regardless.
         .map_err(|err| error!("Error: {}", err))
         .then(|_| ok::<(), DataError>(()))
-        .collect();
-
-    Box::new(pipeline)
+        .collect()
 }
 
 /// Creates a tokio `reactor::Core`, and a `hyper::Client` and
-/// runs the pipeline.
+/// runs the pipeline to completion. The `reactor::Core` is dropped afterwards.
 pub fn run<S>(sources: S, ignore_etags: bool) -> Result<(), DataError>
 where
     S: IntoIterator<Item = Source>,