Index: tango/core/Array.d
===================================================================
--- tango/core/Array.d  (revision 5688)
+++ tango/core/Array.d  (working copy)
@@ -3625,18 +3625,19 @@

        ParameterTupleOf!(Pred)[0][] filter(Array array, Pred pred, ParameterTupleOf!(Pred)[0][] buf = null)
        {
-           // Unfortunately, we don't know our output size -- it could be empty or
-           // the length of the input array. So we won't try to do anything fancy
-           // with preallocation.
-           buf.length = 0;
-           foreach (i, e; array)
+           size_t idx = 0;
+           foreach (e; array)
            {
                if (pred(e))
                {
-                   buf ~= e;
+                   if (idx < buf.length)
+                       buf[idx] = e;
+                   else
+                       buf ~= e;
+                   idx++;
                }
            }
-           return buf;
+           return buf[0..idx];
        }
    }