C++ classes have themselves as implicit inner class

foo.cpp

struct Foo {
  int x;

  Foo() : x(0) {};
  explicit Foo(int x) : x(x) {};

  bool operator>(const Foo& other) const {
    return x > other.x;
  }
};

int main() {
  const Foo a;
  const typename Foo::Foo b(1);
  const typename Foo::Foo::Foo c(2);

  const bool a_gt_b = a > b;
  const bool a_gt_c = a > c;
  const bool b_gt_a = b > a;
  const bool b_gt_c = b > c;
  const bool c_gt_a = c > a;
  const bool c_gt_b = c > b;

  return 0;
}