// immutable object
sclass Bits {
  BitSet bs;
  int n; // length
  
  *() { bs = new BitSet; }
  *(BitSet *bs, int *n) {}
  *(S s) {
    byte[] data = toUtf8(s);
    bs = bytesToBitSet(data);
    n = data.length*8;
  }
  
  byte[] toByteArray() {
    ret bitSetToBytes(bs, n); 
  }
  
  public int hashCode() {
    ret main.hashCode(bs) + n;
  }
  
  public bool equals(O o) {
    if (!o instanceof Bits) false;
    ret n == o/Bits.n && eq(bs, o/Bits.bs);
  }
  
  S getString() {
    ret fromUtf8(toByteArray());
  }
}