added AsRef/Mut impls for 'dyn AsyncWrite + Unpin' when 'S' is 'Unpin' for convenience

src/dual.rs

@@ -17,17 +17,47 @@ use std::{
 bool_type!(pub Encrypted; "Is the value encrypted?");
 bool_type!(pub Encryption; "What way are we en/decrypting?" => Encrypt, Decrypt);
 
+/// A wrapper `AsyncWrite` stream that allows switching between encrypted (chacha20stream) and plain stream writing.
+///
+/// # Polymorphic dispatching
+/// While this type implements `AsyncWrite` itself, it is recommended to use the polymorphic mutable reference returned by `as_dyn_unpin_mut()` (or `as_dyn_mut()` for non-`Unpin` values of `S`) for writing if lots of `AsyncWrite` methods will be dispatched on the instance.
+/// This will prevent the need to check the discriminant of the enum each time the `DualStream`'s `AsyncWrite` methods are polled.
+/// The type implements `AsRef/Mut` for streams `S` that are both `Unpin` and not `Unpin` for convenience.
 #[derive(Debug)]
-pub enum DualStream<S>
+pub enum DualStream<S: AsyncWrite>
 {
     /// If there is a panic while switching modes, the stream is left in this invariant state.
+    ///
+    /// Stream `S` is dropped if the instance is in this state.
     Poisoned,
-    
+
+    /// Stream `S` is being written to through a chacha20stream `AsyncSink` stream cipher.
     Encrypted(AsyncSink<S>),
+    /// Stream `S` is being written to directly.
     Plain(S),
 }
 
-// We can use dynamic dispatching to prevent the need to check the enum's discriminant each time. (In theory. It might not be that useful unless we add `Unpin` here too. TODO: Check this later.)
+// We can use dynamic dispatching to prevent the need to check the enum's discriminant each time.
+// We have `AsRef/Mut`s for normal and `Unpin` polymorphic `AsyncWrite`s 
+impl<'a, S: AsyncWrite + Unpin> AsRef<dyn AsyncWrite + Unpin + 'a> for DualStream<S>
+where S: 'a
+{
+    fn as_ref(&self) -> &(dyn AsyncWrite + Unpin + 'a)
+    {
+	self.as_dyn_unpin()
+    }
+}
+
+impl<'a, S: AsyncWrite + Unpin> AsMut<dyn AsyncWrite + Unpin + 'a> for DualStream<S>
+where S: 'a
+{
+    fn as_mut(&mut self) -> &mut (dyn AsyncWrite + Unpin + 'a)
+    {
+	self.as_dyn_unpin_mut()
+    }
+}
+
+
 impl<'a, S: AsyncWrite> AsRef<dyn AsyncWrite + 'a> for DualStream<S>
 where S: 'a
 {