How Can CRTP Be Used to Achieve Static Polymorphism in C ?

Static Polymorphism via CRTP

To eliminate the performance overhead associated with virtual member functions, C offers the CRTP (Curiously Recurring Template Pattern). This technique facilitates the creation of a statically defined interface for a hierarchy of types, enabling compile-time dispatch.

Alternative Implementations

CRTP can be leveraged in two distinct ways:

1. Static Interface Specification:

<code class="cpp">template <class Derived>
struct base {
  void foo() {
    static_cast<Derived *>(this)->foo();
  };
};</code>

2. Compile-Time Wiring:

<code class="cpp">template <class T>
void bar(base<T> &obj) {
  obj.foo(); // static dispatch
}</code>

Example Usage:

Using these approaches, you can create a statically dispatched interface with compile-time type deduction:

<code class="cpp">struct not_derived_from_base { };

my_type my_instance;
not_derived_from_base invalid_instance;
bar(my_instance); // calls my_instance.foo()
bar(invalid_instance); // compile error (incorrect overload deduction)</code>

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