// Has long indices!
persistable sclass SimpleCircularBuffer<A> is Iterable<A> {
  A[] buffer;
  long base; // elements dropped due to overcapacity
  int size;  // elements actually contained
  
  *(int capacity) {
    buffer = (A[]) new O[capacity];
  }
  
  synchronized void add(A a) {
    if (size == buffer.length) {
      --size;
      ++base;
    }
    buffer[(int) ((base+size) % buffer.length)] = a;
    ++size;
  }
  
  synchronized A get(long pos) {
    if (pos < base || pos >= base+size) null;
    ret buffer[(int) (pos % buffer.length)];
  }
  
  synchronized int size() {
    ret size;
  }
  
  public Iterator<A> iterator() {
    ret new ItIt<A> {
      long i;
      public bool hasNext() { ret i < size(); }
      public A next() { ret get(i++); }
    };
  }
  
  synchronized int capacity() {
    ret buffer.length;
  }
  
  synchronized bool isFull() {
    ret size() == capacity();
  }
  
  bool isEmpty() {
    ret size() == 0;
  }
  
  synchronized long getBase() {
    ret base;
  }
  
  // pop first actually contained element
  synchronized A popFirst() {
    if (isEmpty()) null;
    A a = get(base);
    --size;
    ++base;
    ret a;
  }
}