#include <iostream>
 
template <typename Child>
struct Base
{
    void interface()
    {
        static_cast<Child*>(this)->implementation();
    }
};
 
struct Derived : Base<Derived>
{
    void implementation()
    {
        std::clog << "Derived implementation\n";
    }
};
 
int main()
{
    Derived d;
    d.interface();  // Prints "Derived implementation"
 
    Base<Derived> & statically_polymorphic = d;
    statically_polymorphic.interface();  // Prints "Derived implementation" as well
}
 
 

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