Why is a Virtual Assignment Operator Necessary in C and Can Other Operators Be Made Virtual?

Virtual Assignment Operator in C

The assignment operator in C can be declared virtual, but a fundamental question arises: why is this necessary? And can other operators be made virtual as well?

Is the Assignment Operator Mandatory to be Virtual?

Contrary to popular belief, the assignment operator is not inherently required to be virtual.

Understanding Virtual Functions and Parameter Inheritance

Virtual functions enable polymorphism, allowing derived classes to override base class functions. However, it's crucial to understand that virtual functions are oblivious to parameter inheritance.

Example Demonstrating Parameter Inheritance Limitations:

Consider the following example with classes B and D, where B has an assignment operator virtual and D overrides it:

class B {
public:
  virtual B& operator=(const B& right) {
    x = right.x;
    return *this;
  }

  int x;
};

class D : public B {
public:
  virtual D& operator=(const D& right) {
    x = right.x;
    y = right.y;
    return *this;
  }
  int y;
};

In this scenario, despite the virtual designation of B::operator=, the call is not treated as a virtual function in D because the parameters and return values differ.

Overloaded Operators with Default Values Using Virtual

Although the assignment operator is not inherently virtual, it can be beneficial to define a virtual function that includes default values for derived classes.

class D : public B {
public:
  virtual D& operator=(const D& right) {
    x = right.x;
    y = right.y;
    return *this;
  }

  virtual B& operator=(const B& right) {
    x = right.x;
    y = 13; // Default value
    return *this;
  }

  int y;
};

This approach allows you to assign default values to D objects when assigned to B references.

Employing RTTI for Comprehensive Type Handling

Finally, you can use Run-Time Type Information (RTTI) to handle virtual functions that involve your type effectively.

virtual B& operator=(const B& right) {
  const D *pD = dynamic_cast<const D*>(&right);
  if (pD) {
    x = pD->x;
    y = pD->y;
  } else {
    x = right.x;
    y = 13; // Default value
  }

  return *this;
}

By combining these techniques, you can comprehensively handle assignment operations involving inheritance and ensure proper behavior for derived types.

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