Why Are Pointers/References Essential for Polymorphism in Object-Oriented Programming?

Polymorphism without Pointers/References: An Impossibility

In object-oriented programming, polymorphism enables objects of different classes to respond differently to the same method call. While some questions on StackOverflow touch upon why pointers/references are essential for polymorphism, they often delve into specific scenarios. This article aims to shed light on the fundamental reasons behind the necessity of pointers/references in realizing polymorphism.

It is often assumed that memory allocation on the heap should suffice for dynamic binding, the mechanism that facilitates polymorphism. However, this assumption is incorrect, as demonstrated by the following code:

Derived d;
Base* b = &d;

Here, d is allocated on the stack, yet polymorphism works effectively through the base class pointer b.

Understanding the semantics of polymorphism is crucial. The absence of a base class pointer or reference to a derived class renders polymorphism ineffective. Consider the following:

Base c = Derived();

In this case, the object c is not treated as a Derived but instead as a Base due to slicing. While polymorphism technically applies, it's rendered useless since the original Derived object no longer exists.

Alternatively, the code below highlights the significance of pointers:

Base* c = new Derived();

The pointer c points to a memory location irrespective of whether it references a Base or Derived object. However, calling a virtual method through c triggers dynamic resolution, ensuring polymorphic behavior.

In conclusion, pointers/references are not merely a convenience in implementing polymorphism. They are an intrinsic requirement for maintaining the identity of derived classes and ensuring that virtual method calls resolve to the appropriate implementation. Without pointers/references, polymorphism becomes an impossible concept in object-oriented programming.

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