---

yaml
---
r: 20798
b: refs/heads/snap-stage3
c: 90ce3d9
h: refs/heads/master
v: v3

Author: bblum

[refs]

@@ -1,7 +1,7 @@
 ---
 refs/heads/master: e430a699f2c60890d9b86069fd0c68a70ece7120
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
-refs/heads/snap-stage3: 6fdd1ef9b18039eb29d8c8ba322883a565e94e43
+refs/heads/snap-stage3: 90ce3d94e45233f8aa49e40b1e8a2efc7a0f35ef
 refs/heads/try: ffbe0e0e00374358b789b0037bcb3a577cd218be
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b

branches/snap-stage3/src/libcore/core.rc

@@ -179,6 +179,10 @@ mod option_iter {
 mod result;
 mod to_str;
 mod to_bytes;
+mod util;
+
+// Data structure modules
+
 mod dvec;
 #[path="iter-trait"]
 mod dvec_iter {

branches/snap-stage3/src/libcore/util.rs

@@ -0,0 +1,46 @@
+/**
+ * Miscellaneous helpers for common patterns.
+ */
+
+/**
+ * Swap the values at two mutable locations of the same type, without
+ * deinitialising or copying either one.
+ */
+fn swap<T>(x: &mut T, y: &mut T) {
+    *x <-> *y;
+}
+
+/**
+ * Replace the value at a mutable location with a new one, returning the old
+ * value, without deinitialising or copying either one.
+ */
+fn replace<T>(dest: &mut T, +src: T) -> T {
+    let mut tmp = src;
+    swap(dest, &mut tmp);
+    tmp
+}
+
+/// A non-copyable dummy type.
+class noncopyable {
+    i: ();
+    new() { self.i = (); }
+    drop { }
+}
+
+mod tests {
+    #[test]
+    fn test_swap() {
+        let mut x = 31337;
+        let mut y = 42;
+        swap(&mut x, &mut y);
+        assert x == 42;
+        assert y == 31337;
+    }
+    #[test]
+    fn test_replace() {
+        let mut x = some(noncopyable());
+        let y = replace(&mut x, none);
+        assert x.is_none();
+        assert y.is_some();
+    }
+}