Calling a private method through the vtable

vtable.cpp

#include <iostream>

class A {
  virtual void function() const {
    std::cout << "You bastard!" << std::endl;
  }
};

int main() {
  A a;
  std::size_t * ptr = *(std::size_t **)&a;
  ((void (*)())ptr[0])();
  return 0;
}

Works in clang 3.6 and gcc 5 compiled with -std=c++11 -pedantic -Wall -Wextra.