Add more robust constexpr support

test/optional_test_fwd_header.cpp

@@ -0,0 +1,23 @@
+// Copyright (C) 2026 Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to the Boost Software
+// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//
+// See http://www.boost.org/lib/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  akrzemi1@gmail.com
+
+#include "boost/optional/optional_fwd.hpp"
+#include "boost/optional/optional.hpp"
+
+void statically_test_basic_instantiations()
+{
+  boost::optional<int> oN, o1(1);
+  swap(oN, o1);
+
+  int i = 1;
+  boost::optional<int> rN, ri(i);
+  swap(rN, ri);
+}