it is possible to change return type when override a virtual function in C++?

Question

I encounter a problems about override virtual functions, in fact,it is about hessian (a web service protocol).

it has a base class Object, and some derived classes :

Answer 1

Regarding @MerickOWA comment, here's another solution, that does not requires any additional template mechanism.

Since you intended to have a virtual "value()" method that you needed to implement in all classes, I've extended the idea (usually, in these kind of framework, you've plenty of similar "basic" methods, so I've used a macro to write them for me, it's not required, it's just faster and less error prone.

#include 
#include 
#include 

struct Object
{
   std::string toString() const { std::ostringstream str; getValue(str); return str.str(); }
   virtual void getValue(std::ostringstream & str) const { str<<"BadObj"; }
};

// Add all the common "basic & common" function here
#define __BoilerPlate__     basic_type value; void getValue(std::ostringstream & str) const { str << value; }
// The only type specific part
#define MAKE_OBJ(T)         typedef T basic_type;      __BoilerPlate__

struct Long : public Object
{
   MAKE_OBJ(long long)
   Long() : value(345) {}
};

struct Int : public Object
{
   MAKE_OBJ(long)
   Int() : value(3) {}
};

int main()
{
    Object a;
    Long b;
    Int c;
    std::cout<

Obviously, the trick is in the std::ostringstream classes that's accept any parameter type (long long, long, etc...). Since this is standard C++ practice, it should not matter.