/// @brief visit an object (non-const)
///
/// @param b
///
/// This function is called upon visitation.
///
/// It extracts the correct thunk from the vtable and calls it
result_type operator()
(
base_type & b
)
{
// fetch thunk
func_type thunk = (*_vtable)[ b.tag() ];
// call thunk: pointer to member function syntac
return
( this->*thunk )
(
b
);
}
