Merge pull request #499 from rkarp/trait-asserts

Make trait assertions nicer

Author: alexcrichton

futures-cpupool/src/lib.rs

@@ -89,12 +89,8 @@ struct MySender<F, T> {
     keep_running_flag: Arc<AtomicBool>,
 }
 
-fn _assert() {
-    fn _assert_send<T: Send>() {}
-    fn _assert_sync<T: Sync>() {}
-    _assert_send::<CpuPool>();
-    _assert_sync::<CpuPool>();
-}
+trait AssertSendSync: Send + Sync {}
+impl AssertSendSync for CpuPool {}
 
 struct Inner {
     tx: Mutex<mpsc::Sender<Message>>,

src/sync/mpsc/mod.rs

@@ -106,14 +106,8 @@ pub struct Sender<T> {
 #[derive(Debug)]
 pub struct UnboundedSender<T>(Sender<T>);
 
-fn _assert_kinds() {
-    fn _assert_send<T: Send>() {}
-    fn _assert_sync<T: Sync>() {}
-    fn _assert_clone<T: Clone>() {}
-    _assert_send::<UnboundedSender<u32>>();
-    _assert_sync::<UnboundedSender<u32>>();
-    _assert_clone::<UnboundedSender<u32>>();
-}
+trait AssertKinds: Send + Sync + Clone {}
+impl AssertKinds for UnboundedSender<u32> {}
 
 
 /// The receiving end of a channel which implements the `Stream` trait.

src/task_impl/atomic_task.rs

@@ -43,8 +43,8 @@ impl AtomicTask {
     /// Create an `AtomicTask` initialized with the given `Task`
     pub fn new() -> AtomicTask {
         // Make sure that task is Sync
-        fn is_sync<T: Sync>() {}
-        is_sync::<Task>();
+        trait AssertSync: Sync {}
+        impl AssertSync for Task {}
 
         AtomicTask {
             state: AtomicUsize::new(WAITING),

src/task_impl/mod.rs

@@ -61,10 +61,8 @@ pub struct Task {
     events: UnparkEvents,
 }
 
-fn _assert_kinds() {
-    fn _assert_send<T: Send>() {}
-    _assert_send::<Task>();
-}
+trait AssertSend: Send {}
+impl AssertSend for Task {}
 
 /// Returns a handle to the current task to call `notify` at a later date.
 ///

tests/mpsc.rs

@@ -11,13 +11,9 @@ use std::thread;
 use std::sync::{Arc, Mutex};
 use std::sync::atomic::{AtomicUsize, Ordering};
 
-fn is_send<T: Send>() {}
-
-#[test]
-fn bounds() {
-    is_send::<mpsc::Sender<i32>>();
-    is_send::<mpsc::Receiver<i32>>();
-}
+trait AssertSend: Send {}
+impl AssertSend for mpsc::Sender<i32> {}
+impl AssertSend for mpsc::Receiver<i32> {}
 
 #[test]
 fn send_recv() {

tests/ready_queue.rs

@@ -8,14 +8,8 @@ use futures::future;
 use futures::stream::FuturesUnordered;
 use futures::sync::oneshot;
 
-#[test]
-fn bounds() {
-    fn is_send<T: Send>() {}
-    fn is_sync<T: Sync>() {}
-
-    is_send::<FuturesUnordered<()>>();
-    is_sync::<FuturesUnordered<()>>();
-}
+trait AssertSendSync: Send + Sync {}
+impl AssertSendSync for FuturesUnordered<()> {}
 
 #[test]
 fn basic_usage() {