What are the Different Types and Mechanisms of Polymorphism in C ?

Understanding Polymorphism in C

Polymorphism allows you to write code that can work with different types of data without explicitly specifying each type. C provides multiple mechanisms for achieving polymorphism:

Explicit Polymorphism

Overloading:

void f(int x); // overload for int
void f(double x); // overload for double

Templates:

template <typename T>
void f(T& x); // template for any type T

Virtual Dispatch:

struct Base {
    virtual void g() = 0; // pure virtual function
};

struct X : Base {
    virtual void g() { // overrides g() for X
        // ...
    }
};

// ...

void h(Base& b) {
    b.g(); // run-time polymorphic call
}

Other Polymorphism Types

Ad-hoc Polymorphism

Used when the number of supported types is limited and must be explicitly specified.

Parametric Polymorphism

Used when the code is written generically without specifying specific types, allowing it to work with any new type.

Terminology and Categorization

Further Categorization

By Timing:

• Run-Time Polymorphism: Polymorphic code is resolved at run time.
• Compile-Time Polymorphism: Polymorphic code is resolved during compilation.

By Supported Types:

• Ad-hoc Polymorphism: Supports a finite number of specified types.
• Parametric Polymorphism: Supports any type that meets certain criteria.
• Subtype Polymorphism: Supports inheritance hierarchies.

"Polymorphic" Definition

In the C Standard, "polymorphic" refers only to run-time polymorphism using virtual dispatch. In general computing science, "polymorphic" has a broader meaning.

Considerations and Discussion

• Choose the appropriate polymorphism mechanism based on the specific needs of your code.
• Run-time polymorphism may introduce overhead compared to compile-time polymorphism.
• Compiler-provided type extensions and Standard conversions contribute to the ease of implementing polymorphism.
• Parametric polymorphism allows for code reuse and abstraction without requiring type-specific code.

Conclusion

Polymorphism in C enables the creation of reusable, type-agnostic code that can be applied to a wide range of data types. By understanding the different types and mechanisms available, you can effectively leverage polymorphism to improve the flexibility and efficiency of your code.

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