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Polymorphism

 

Recall that polymorphism is the phenomenon where the same message sent to two different objects produces two different set of actions. Polymorphism is broadly divided into two parts:

 

  • Static polymorphism exhibited by overloaded functions.
  • Dynamic polymorphism exhibited by using late binding.

 

Static Polymorphism

 

Static polymorphism refers to an entity existing in different physical forms simultaneously. Static polymorphism involves binding of functions based on the number, type, and sequence of arguments. The various types of parameters are specified in the function declaration, and therefore the function can be bound to calls at compile time. This form of association is called early binding. The term early binding stems from the fact that when the program is executed, the calls are already bound to the appropriate functions.

 

The resolution of a function call is based on number, type, and sequence of arguments declared for each form of the function. Consider the following function declaration:

 

            void add(int , int);

            void add(float, float);

 

When the add() function is invoked, the parameters passed to it will determine which version of the function will be executed. This resolution is done at compile time.

 

Dynamic Polymorphism

 

Dynamic polymorphism refers to an entity changing its form depending on the circumstances. A function is said to exhibit dynamic polymorphism when it exists in more than one form, and calls to its various forms are resolved dynamically when the program is executed. The term late binding  refers to the resolution of the functions at run-time instead of compile time. This feature increases the flexibility of the program by allowing the appropriate method to be invoked, depending on the context.

 

Static Vs Dynamic Polymorphism

 

Static polymorphism is considered more efficient, and dynamic polymorphism more flexible.

 

Statically bound methods are those methods that are bound to their calls at compile time. Dynamic function calls are bound to the functions during run-time. This involves the additional step of searching the functions during run-time. On the other hand, no run-time search is required for statically bound functions.

As applications are becoming larger and more complicated, the need for flexibility is increasing rapidly. Most users have to periodically upgrade their software, and this could become a very tedious task if static polymorphism is applied. This is because any change

in requirements requires a major modification in the code. In the case of dynamic binding, the function calls are resolved at run-time, thereby giving the user the flexibility to alter the call without having to modify the code.

 

To the programmer, efficiency and performance would probably be a primary concern, but to the user, flexibility or maintainability may be much more important. The decision is thus a trade-off between efficiency and flexibility.

 

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