anchor.diff:    }
   
     T last() {
  -    if (length === 0) {
  -      throw new IndexOutOfRangeException(-1);
  -    }
       return this[length - 1];
     }
   
  
positive.code:     this.length = newLength;
      return result;
    }
    
    void setRange(int start, int length, List<T> from, [int startFrom = 0]) {
      if (length < 0) {
        throw new IllegalArgumentException("negative length $length");
  
negative.code: 
    T removeLast() {
      var len = length - 1;
      var elem = this[len];
      this[len] = null;
      _setLength(len);
  