---

yaml
---
r: 144309
b: refs/heads/try2
c: 598072a
h: refs/heads/master
i:
  144307: 6b64e7a
v: v3

Author: bblum

[refs]

@@ -5,7 +5,7 @@ refs/heads/snap-stage3: 78a7676898d9f80ab540c6df5d4c9ce35bb50463
 refs/heads/try: 519addf6277dbafccbb4159db4b710c37eaa2ec5
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b
-refs/heads/try2: b81f5c547c41571be3814ad4b2802f3305e12152
+refs/heads/try2: 598072afa46d3c4fca7659c49ef3c9dc9f85787e
 refs/heads/dist-snap: ba4081a5a8573875fed17545846f6f6902c8ba8d
 refs/tags/release-0.2: c870d2dffb391e14efb05aa27898f1f6333a9596
 refs/tags/release-0.3: b5f0d0f648d9a6153664837026ba1be43d3e2503

branches/try2/src/libstd/cell.rs

@@ -50,6 +50,12 @@ impl<T> Cell<T> {
         this.value.take_unwrap()
     }
 
+    /// Yields the value if the cell is full, or `None` if it is empty.
+    pub fn take_opt(&self) -> Option<T> {
+        let this = unsafe { transmute_mut(self) };
+        this.value.take()
+    }
+
     /// Returns the value, failing if the cell is full.
     pub fn put_back(&self, value: T) {
         let this = unsafe { transmute_mut(self) };

branches/try2/src/libstd/rt/comm.rs

@@ -499,13 +499,14 @@ impl<T> GenericPort<T> for Port<T> {
     }
 
     fn try_recv(&self) -> Option<T> {
-        let pone = self.next.take();
-        match pone.try_recv() {
-            Some(StreamPayload { val, next }) => {
-                self.next.put_back(next);
-                Some(val)
+        do self.next.take_opt().map_move_default(None) |pone| {
+            match pone.try_recv() {
+                Some(StreamPayload { val, next }) => {
+                    self.next.put_back(next);
+                    Some(val)
+                }
+                None => None
             }
-            None => None
         }
     }
 }