struct B1 {
  int i;
  double d;
};

struct B2 {
  struct B1 b1;
  float f;
} b2;

int main(void) {
  struct B2 * p = &b2;
  int * q = (int *)p;
  *q = 10;
  $assert(b2.b1.i == 10);
}