#include <boost/spirit/include/qi.hpp>

int main()
{
  using namespace boost::spirit::qi;
 
  typedef std::string::iterator iter;
 
  rule<iter, int()> a;
  rule<iter, int()> a_cp;
  a_cp = a;           //compiles       
  a_cp = a.copy();    //compiles
  a_cp = a.alias();   //compiles
 
  rule<iter, int(int)> b;
  rule<iter, int(int)> b_cp;
  b_cp = b;           //compiles
  b_cp = b.copy();    //fails to compile
  b_cp = b.alias();   //fails to compile
}