struct B1 {
  int i;
  double d;
};

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

int main(void) {
  int * p = &b2.b1.i;
  struct B2 * q = (struct B2 *)p;
  *q = (struct B2) { { 2, 3.14 }, 2.718 };
  $assert(b2.b1.i == 2);
  $assert(b2.b1.d == 3.14);
  $assert(b2.f == 2.718);
}