#include <stdio.h>

template<typename T>
class Base 
{
public:
  void BaseMethod()
  {
    static_cast<T*>(this)->DerivedMethod2();
  }
};

class Derived : private Base<Derived>
{
public:
  void DerivedMethod1()
  {
    BaseMethod();
  }

  void DerivedMethod2()
  {
    printf("here\n");
  }

private:
  friend Base<Derived>; //Line 27: error: a class-key must be used when declaring a friend
};

int main()
{
  Derived d;
  d.DerivedMethod1();
}