How to write a Java-enum-like class with multiple data fields in C++?

Question

Coming from a Java background, I find C++\'s enums very lame. I wanted to know how to write Java-like enums (the ones in which the enum values are objects, and can have attr

Answer 1

This is ugly, verbose, and generally a dumb way to go. But I figured I'd post a complete code example by way of explanation. For extra points it's actually possible to define a compile-time expanded iteration over the solar planets by tweaking the template specializations just a tad.

#include 
#include 
#include 
#include 

class Planet {
 public:
   static const double G = 6.67300E-11;

   Planet(const ::std::string &name, double mass, double radius)
        : name_(name), mass_(mass), radius_(radius)
      {}
   const ::std::string &name() const { return name_; }
   double surfaceGravity() const {
      return G * mass_ / (radius_ * radius_);
   }
   double surfaceWeight(double otherMass) const {
      return otherMass * surfaceGravity();
   }

 private:
   const ::std::string name_;
   const double mass_;
   const double radius_;
};

enum SolarPlanets {
   MERCURY,
   VENUS,
   EARTH,
   MARS,
   JUPITER,
   SATURN,
   URANUS,
   NEPTUNE
};

template 
class SolarPlanet : public Planet {
};

template <>
class SolarPlanet : public Planet {
 public:
   SolarPlanet() : Planet("MERCURY", 3.303e+23, 2.4397e6) {}
};

template <>
class SolarPlanet : public Planet {
 public:
   SolarPlanet() : Planet("VENUS", 4.869e+24, 6.0518e6) {}
};

template <>
class SolarPlanet : public Planet {
 public:
   SolarPlanet() : Planet("EARTH", 5.976e+24, 6.37814e6) {}
};

template <>
class SolarPlanet : public Planet {
 public:
   SolarPlanet() : Planet("MARS", 6.421e+23, 3.3972e6) {}
};

template <>
class SolarPlanet : public Planet {
 public:
   SolarPlanet() : Planet("JUPITER", 1.9e+27, 7.1492e7 ) {}
};

template <>
class SolarPlanet : public Planet {
 public:
   SolarPlanet() : Planet("SATURN", 5.688e+26, 6.0268e7) {}
};

template <>
class SolarPlanet : public Planet {
 public:
   SolarPlanet() : Planet("URANUS", 8.686e+25, 2.5559e7) {}
};

template <>
class SolarPlanet : public Planet {
 public:
   SolarPlanet() : Planet("NEPTUNE", 1.024e+26, 2.4746e7) {}
};

void printTerranWeightOnPlanet(
   ::std::ostream &os, double terran_mass, const Planet &p
   )
{
   const double mass = terran_mass / SolarPlanet().surfaceGravity();
   os << "Your weight on " << p.name() << " is " << p.surfaceWeight(mass) << '\n';
}

int main(int argc, const char *argv[])
{
   if (argc != 2) {
      ::std::cerr << "Usage: " << argv[0] << " \n";
      return 1;
   }
   const double earthweight = ::std::atof(argv[1]);
   printTerranWeightOnPlanet(::std::cout, earthweight, SolarPlanet());
   printTerranWeightOnPlanet(::std::cout, earthweight, SolarPlanet());
   printTerranWeightOnPlanet(::std::cout, earthweight, SolarPlanet());
   printTerranWeightOnPlanet(::std::cout, earthweight, SolarPlanet());
   printTerranWeightOnPlanet(::std::cout, earthweight, SolarPlanet());
   printTerranWeightOnPlanet(::std::cout, earthweight, SolarPlanet());
   printTerranWeightOnPlanet(::std::cout, earthweight, SolarPlanet());
   printTerranWeightOnPlanet(::std::cout, earthweight, SolarPlanet());
   return 0;
}