Add implicit conversion between compatible reference wrappers (refs #83)

test/ref_conversion_test.cpp

@@ -0,0 +1,39 @@
+//  Implicit conversions between compatible reference wrappers
+//
+//  Copyright 2020 Peter Dimov
+//
+//  Distributed under 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
+
+#include <boost/ref.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+struct X
+{
+};
+
+struct Y: public X
+{
+};
+
+void f1( boost::reference_wrapper<X> r, Y * p )
+{
+    BOOST_TEST_EQ( r.get_pointer(), p );
+}
+
+void f2( boost::reference_wrapper<int const> r, int * p )
+{
+    BOOST_TEST_EQ( r.get_pointer(), p );
+}
+
+int main()
+{
+    Y y;
+    f1( boost::ref(y), &y );
+
+    int i = 0;
+    f2( boost::ref(i), &i );
+
+    return boost::report_errors();
+}