What's the use of the derived class as a template parameter?

Question

What's the purpose of this pattern? What is it called? It looked very strange when I saw it the first time, though I have now seen it many times.

template<typename Derived>
struct Base {
  //...
};

struct Example : Base<Example> {
  //...
};

Answer 1

It's called the Curiously Recurring Template pattern, and allows for static polymorphism.

It's useful when you want to add functionality to a specific class, but want the utility to be usable in a generic case. By making the utility dependent on and use a template parameter, you can achieve both.

Answer 2

I think you are reffering to CRTP. Also refer here