Question

I understand how polymorphism and inheritance works in C++, but my problem is: how do you make operators polymorphic for the following specific example?

Say I have a Foo class and two Foo instances, fooA and fooB. I want to redefine the plus sign operator so that “fooA + fooB;” does something specific to Foo instances (whatever that may be). How would the function prototype look? It’s confusing me because I’m used to functions starting with a letter… Any help would be greatly appreciated.

By the way, this isn’t a homework question — more like a wonderment (I was thinking about polymorphism in Ruby).

Answer 1

Example from http://publib.boulder.ibm.com/infocenter/comphelp/v8v101/topic/com.ibm.xlcpp8a.doc/language/ref/cplr318.htm:

#include <iostream>
using namespace std;

class complx 
{
      double real, imag;
public:
      complx(double real = 0., double imag = 0.); // constructor
      complx operator+(const complx&) const;      // operator+()
};

// define constructor
complx::complx(double r, double i)
{
      real = r; imag = i;
}

// define overloaded + (plus) operator
complx complx::operator+(const complx& c) const
{
      complx result;
      result.real = this->real + c.real;
      result.imag = this->imag + c.imag;
      return result;
}

int main()
{
      complx x(4,4);
      complx y(6,6);
      complx z = x + y; // calls complx::operator+()
}