[boost] [variant] static_visitor has no virtual destructor.

Hello, I have a compilation error with Boost (1.52) and g++ (4.7) with the flag -Weffc++: error: base class ‘class boost::static_visitor<std::basic_string<char>

’ has a non-virtual destructor [-Werror=effc++]

And the static_visitor class is defined with a protected non-virtual destructor: template <typename R = ::boost::detail::static_visitor_default_return> class static_visitor : public detail::is_static_visitor_tag { public: // typedefs typedef R result_type; protected: // for use as base class only static_visitor() { } ~static_visitor() { } }; Is it normal ? And if it is, how to avoid this error ? Thank you for your help, Pierre Talbot.