Added utils::variant_index

src/utils/variant.hpp

@@ -1,14 +1,14 @@
 /*
-   Copyright (C) 2021 by the Battle for Wesnoth Project https://www.wesnoth.org/
+	Copyright (C) 2021 by the Battle for Wesnoth Project https://www.wesnoth.org/
 
-   This program is free software; you can redistribute it and/or modify
-   it under the terms of the GNU General Public License as published by
-   the Free Software Foundation; either version 2 of the License, or
-   (at your option) any later version.
-   This program is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY.
+	This program is free software; you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation; either version 2 of the License, or
+	(at your option) any later version.
+	This program is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY.
 
-   See the COPYING file for more details.
+	See the COPYING file for more details.
 */
 
 #pragma once
@@ -68,4 +68,15 @@ inline T* get_if(V* variant)
 }
 
 #endif
+
+template<typename... Types>
+std::size_t variant_index(const variant<Types...>& var)
+{
+#ifndef USING_BOOST_VARIANT
+	return var.index();
+#else
+	return var.which();
+#endif
+}
+
 } // namespace utils