expose try_recv and try_send on channels

Signed-off-by: Yoshua Wuyts <yoshuawuyts@gmail.com>

src/sync/channel.rs

@@ -1,5 +1,6 @@
 use std::cell::UnsafeCell;
-use std::fmt;
+use std::error::Error;
+use std::fmt::{Debug, Display, self};
 use std::future::Future;
 use std::isize;
 use std::marker::PhantomData;
@@ -192,6 +193,27 @@ impl<T> Sender<T> {
         .await
     }
 
+    /// Attempts to send a message into the channel.
+    ///
+    /// If the channel is full, this method will return an error.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # async_std::task::block_on(async {
+    /// #
+    /// use async_std::sync::channel;
+    ///
+    /// let (s, r) = channel(1);
+    /// assert!(s.try_send(1).is_ok());
+    /// assert!(s.try_send(2).is_err());
+    /// #
+    /// # })
+    /// ```
+    pub fn try_send(&self, msg: T) -> Result<(), TrySendError<T>> {
+        self.channel.try_send(msg)
+    }
+
     /// Returns the channel capacity.
     ///
     /// # Examples
@@ -409,6 +431,30 @@ impl<T> Receiver<T> {
         .await
     }
 
+    /// Attempts to receive a message from the channel.
+    ///
+    /// If the channel is empty, this method will return an error.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # async_std::task::block_on(async {
+    /// #
+    /// use async_std::sync::channel;
+    ///
+    /// let (s, r) = channel(1);
+    ///
+    /// s.send(1u8).await;
+    ///
+    /// assert!(r.try_recv().is_ok());
+    /// assert!(r.try_recv().is_err());
+    /// #
+    /// # })
+    /// ```
+    pub fn try_recv(&self) -> Result<T, TryRecvError> {
+        self.channel.try_recv()
+    }
+
     /// Returns the channel capacity.
     ///
     /// # Examples
@@ -936,8 +982,8 @@ impl<T> Drop for Channel<T> {
     }
 }
 
-/// An error returned from the `try_send()` method.
-enum TrySendError<T> {
+/// An error returned from the `try_send` method.
+pub enum TrySendError<T> {
     /// The channel is full but not disconnected.
     Full(T),
 
@@ -945,11 +991,43 @@ enum TrySendError<T> {
     Disconnected(T),
 }
 
-/// An error returned from the `try_recv()` method.
-enum TryRecvError {
+impl<T> Error for TrySendError<T> {}
+
+impl<T> Debug for TrySendError<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Full(_) => Debug::fmt("Full<T>", f),
+            Self::Disconnected(_) => Debug::fmt("Disconnected<T>", f),
+        }
+    }
+}
+
+impl<T> Display for TrySendError<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Full(_) => Display::fmt("The channel is full.", f),
+            Self::Disconnected(_) => Display::fmt("The channel is full and disconnected.", f),
+        }
+    }
+}
+
+/// An error returned from the `try_recv` method.
+#[derive(Debug)]
+pub enum TryRecvError {
     /// The channel is empty but not disconnected.
     Empty,
 
     /// The channel is empty and disconnected.
     Disconnected,
 }
+
+impl Error for TryRecvError {}
+
+impl Display for TryRecvError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Empty => Display::fmt("The channel is empty.", f),
+            Self::Disconnected => Display::fmt("The channel is empty and disconnected.", f),
+        }
+    }
+}

src/sync/mod.rs

@@ -184,7 +184,7 @@ mod rwlock;
 
 cfg_unstable! {
     pub use barrier::{Barrier, BarrierWaitResult};
-    pub use channel::{channel, Sender, Receiver};
+    pub use channel::{channel, Sender, Receiver, TryRecvError, TrySendError};
 
     mod barrier;
     mod channel;