---

yaml
---
r: 28150
b: refs/heads/try
c: 3e4b558
h: refs/heads/master
v: v3

Author: jld

[refs]

@@ -2,7 +2,7 @@
 refs/heads/master: cd6f24f9d14ac90d167386a56e7a6ac1f0318195
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
 refs/heads/snap-stage3: cd6f24f9d14ac90d167386a56e7a6ac1f0318195
-refs/heads/try: 5eef15df126e8dfedc9e72ee3d9456ead0c9d06d
+refs/heads/try: 3e4b55807d9778c396ae449fe9a5680508d7d62d
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b
 refs/heads/try2: d0c6ce338884ee21843f4b40bf6bf18d222ce5df

branches/try/src/libcore/vec.rs

@@ -42,6 +42,7 @@ export push, push_all, push_all_move;
 export grow;
 export grow_fn;
 export grow_set;
+export truncate;
 export map;
 export mapi;
 export map2;
@@ -611,6 +612,20 @@ fn push_all_move<T>(&v: ~[const T], -rhs: ~[const T]) {
     }
 }
 
+/// Shorten a vector, dropping excess elements.
+fn truncate<T>(&v: ~[const T], newlen: uint) {
+    do as_buf(v) |p, oldlen| {
+        assert(newlen <= oldlen);
+        unsafe {
+            // This loop is optimized out for non-drop types.
+            for uint::range(newlen, oldlen) |i| {
+                let _dropped <- *ptr::offset(p, i);
+            }
+            unsafe::set_len(v, newlen);
+        }
+    }
+}
+
 // Appending
 #[inline(always)]
 pure fn append<T: copy>(+lhs: ~[T], rhs: &[const T]) -> ~[T] {
@@ -2166,6 +2181,15 @@ mod tests {
         assert (v[4] == 5);
     }
 
+    #[test]
+    fn test_truncate() {
+        let mut v = ~[@6,@5,@4];
+        truncate(v, 1);
+        assert(v.len() == 1);
+        assert(*(v[0]) == 6);
+        // If the unsafe block didn't drop things properly, we blow up here.
+    }
+
     #[test]
     fn test_map() {
         // Test on-stack map.