Boosts variant library has a solution to this problem http://www.boost.org/doc/libs/1_65_1/doc/html/variant/tutorial.html#variant.tutorial.recursive http://www

Boosts variant library has a solution to this problem http://www.boost.org/doc/libs/1_65_1/doc/html/variant/tutorial.html#variant.tutorial.recursive http://www.boost.org/doc/libs/1_65_1/doc/html/variant/tutori... boost::variant< int, boost::recursive_wrapper<binary_op<add>>, boost::recursive_wrapper<binary_op<sub>> > expression; When the visitor is applied, the recursive wrappers are unwrapped transparently.