Should C Assignment Operators Be Virtual?

Virtual Assignment Operator and Its Necessities in C

While assignment operators can be defined as virtual in C , it's not a mandatory requirement. However, this virtual declaration raises questions about the need for virtuality and whether other operators can be made virtual as well.

The Case for Virtual Assignment Operator

The assignment operator is not inherently virtual. However, it becomes necessary when assigning objects of inherited classes to base class variables. This dynamic binding ensures that the correct implementation of the assignment operator based on the dynamic type of the object is called.

Can Other Operators Be Virtual?

Yes, other operators that take as arguments an object of the type being defined can also be made virtual. This allows for runtime binding of these operators, ensuring that the correct implementation is used based on the dynamic type of the object.

Unexpected Behavior with Virtual Assignment Operator

Making the assignment operator virtual can lead to unexpected behavior. A virtual function's signature must be identical for all its overrides. Therefore, it's important to ensure that the parameters and return values of overridden assignment operators for different classes are consistent.

Default Values and Overloaded Assignment Operators

Default values for parameters in assignment operators can be implemented through virtual functions. This allows default values to be used when an object of an inherited class is assigned to a variable of the base class type.

Runtime Type Information (RTTI)

RTTI can be utilized to handle assignment operators for inherited types effectively. By using dynamic_cast to determine the type of the incoming object, the correct assignment operator implementation can be executed.

Example: Assigning D Objects to B Objects

Consider the following code:

class B {
public:
  virtual void operator=(const B& right) { ... }
  int x;
};

class D : public B {
public:
  virtual void operator=(const B& right) { ... }
  int y;
};

Without virtuality, assigning a D object to a B object would call the assignment operator from class B, which wouldn't correctly handle the additional data member in class D. However, with virtuality, the correct assignment operator from class D is called.

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