error

from /home/alonsoj1/ros_workspace/prueba/src/twist_subscriber.cpp:1:
  /usr/include/boost/function/function_template.hpp: In static member function ‘static void boost::detail::function::void_function_invoker1<FunctionPtr, R, T0>::invoke(boost::detail::function::function_buffer&, T0) [with FunctionPtr = void (*)(const boost::shared_ptr<const std_msgs::String_<std::allocator<void> > >&), R = void, T0 = const boost::shared_ptr<const geometry_msgs::Twist_<std::allocator<void> > >&]’:
  /usr/include/boost/function/function_template.hpp:913:   instantiated from ‘void boost::function1<R, T1>::assign_to(Functor) [with Functor = void (*)(const boost::shared_ptr<const std_msgs::String_<std::allocator<void> > >&), R = void, T0 = const boost::shared_ptr<const geometry_msgs::Twist_<std::allocator<void> > >&]’
  /usr/include/boost/function/function_template.hpp:722:   instantiated from ‘boost::function1<R, T1>::function1(Functor, typename boost::enable_if_c<boost::type_traits::ice_not::value, int>::type) [with Functor = void (*)(const boost::shared_ptr<const std_msgs::String_<std::allocator<void> > >&), R = void, T0 = const boost::shared_ptr<const geometry_msgs::Twist_<std::allocator<void> > >&]’
  /usr/include/boost/function/function_template.hpp:1064:   instantiated from ‘boost::function<R(T0)>::function(Functor, typename boost::enable_if_c<boost::type_traits::ice_not::value, int>::type) [with Functor = void (*)(const boost::shared_ptr<const std_msgs::String_<std::allocator<void> > >&), R = void, T0 = const boost::shared_ptr<const geometry_msgs::Twist_<std::allocator<void> > >&]’
  /home/alonsoj1/ros_workspace/prueba/src/twist_subscriber.cpp:15:   instantiated from here
  /usr/include/boost/function/function_template.hpp:112: error: invalid initialization of reference of type ‘const boost::shared_ptr<const std_msgs::String_<std::allocator<void> > >&’ from expression of type ‘const boost::shared_ptr<const geometry_msgs::Twist_<std::allocator<void> > >’
  make[3]: *** [CMakeFiles/twist_subscriber.dir/src/twist_subscriber.o] Error 1
  make[3]: Leaving directory `/home/alonsoj1/ros_workspace/prueba/build'
  make[2]: *** [CMakeFiles/twist_subscriber.dir/all] Error 2
  make[2]: Leaving directory `/home/alonsoj1/ros_workspace/prueba/build'
  make[1]: *** [all] Error 2
  make[1]: Leaving directory `/home/alonsoj1/ros_workspace/prueba/build'