1 files changed, 35 insertions, 0 deletions
diff --git a/include/o3tl/unsafe_downcast.hxx b/include/o3tl/unsafe_downcast.hxx
new file mode 100644
index 000000000..b49994eff
--- /dev/null
+++ b/include/o3tl/unsafe_downcast.hxx
@@ -0,0 +1,35 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef INCLUDED_O3TL_UNSAFE_DOWNCAST_HXX
+#define INCLUDED_O3TL_UNSAFE_DOWNCAST_HXX
+
+#include <cassert>
+#include <type_traits>
+
+namespace o3tl
+{
+// Do a downcast from polymorphic `BasePtr` to `DerivedPtr` when it is known that `p` is actually
+// pointing to an object of derived type (or is a nullptr).  This is potentially cheaper than
+// dynamic_cast and helps to avoid Coverity warnings about unchecked dynamic_cast.
+template <typename DerivedPtr, typename BasePtr>
+std::enable_if_t<
+    (std::is_pointer_v<
+         DerivedPtr> && std::is_pointer_v<BasePtr> && std::is_base_of_v<std::remove_pointer_t<BasePtr>, std::remove_pointer_t<DerivedPtr>>),
+    DerivedPtr>
+unsafe_downcast(BasePtr p)
+{
+    assert(p == nullptr || dynamic_cast<DerivedPtr>(p) != nullptr);
+    return static_cast<DerivedPtr>(p);
+}
+}
+
+#endif
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */