#include <boost/variant.hpp>

class b_fwd;

typedef
    boost::variant
    <
        boost::recursive_wrapper<b_fwd>
    >
    a
;



class c_fwd;

typedef
    boost::variant
    <
        boost::recursive_wrapper<c_fwd>
    >
    b
;
struct b_fwd: b
{
    //inherit constructors
    template<typename... Ts>
    b_fwd(Ts... o): b(o...){}
};



typedef
    boost::variant
    <
        double,
        char*
    >
    c
;
struct c_fwd: c
{
    //inherit constructors
    template<typename... Ts>
    c_fwd(Ts... o): c(o...){}
};



void
f(const b& b_node)
{
    a a_node(b_node);
}



int main()
{
}