--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libphobos/libdruntime/rt/invariant.d	Thu Feb 13 11:34:05 2020 +0900
@@ -0,0 +1,36 @@
+/**
+ * Implementation of invariant support routines.
+ *
+ * Copyright: Copyright Digital Mars 2007 - 2010.
+ * License:   $(WEB www.boost.org/LICENSE_1_0.txt, Boost License 1.0).
+ * Authors:   Walter Bright
+ */
+
+/*          Copyright Digital Mars 2007 - 2010.
+ * Distributed under the Boost Software License, Version 1.0.
+ *    (See accompanying file LICENSE or copy at
+ *          http://www.boost.org/LICENSE_1_0.txt)
+ */
+
+
+/**
+ *
+ */
+void _d_invariant(Object o)
+{   ClassInfo c;
+
+    //printf("__d_invariant(%p)\n", o);
+
+    // BUG: needs to be filename/line of caller, not library routine
+    assert(o !is null); // just do null check, not invariant check
+
+    c = typeid(o);
+    do
+    {
+        if (c.classInvariant)
+        {
+            (*c.classInvariant)(o);
+        }
+        c = c.base;
+    } while (c);
+}