Can CRTP Replace Virtual Functions for Static Polymorphism in C ?

Static Polymorphism with CRTP

In C , virtual member functions provide a mechanism for implementing polymorphism. However, they come with an overhead due to dynamic binding. This article explores the use of Curiously Recurring Template Pattern (CRTP) as an alternative to avoid this overhead.

CRTP Approach

To implement static polymorphism using CRTP, two techniques can be employed:

Static Interface Definition

The first approach involves statically defining the interface for the structure of types. By using CRTP, the base class template specifies the interface, and derived classes must implement the required member functions. The base class uses a static cast to invoke the appropriate function in derived classes, eliminating the need for virtual functions.

Compile-Time Type Deduction

The second technique dispenses with pointer-to-base or reference-to-base idioms and performs the wiring at compile time. The base class template is defined, and template functions are used to perform static dispatch based on the deduced type of the base class parameter.

Benefits

CRTP with static polymorphism offers several benefits:

• Elimination of dynamic binding overhead
• Improved performance, especially in scenarios with frequent polymorphism
• Increased code readability and maintenance

Example

Here's a simplified example demonstrating the first approach using CRTP:

<code class="cpp">template <class derived>
struct Base {
  void foo() {
    static_cast<derived>(this)->foo();
  }
};

struct MyType : Base<mytype> {
  void foo() {
    // Implementation
  }
};</mytype></derived></class></code>

This example avoids the use of virtual functions and performs static dispatch based on the type of the derived class.

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