kFree = 1,
    kRead = 2,
    kWrite = 3
  };

 public:
  bool IsAlloc() const { return effects_.test(kAlloc); }
  bool IsFree() const { return effects_.test(kFree); }
  bool IsRead() const { return effects_.test(kRead); }
  bool IsWrite() const { return effects_.test(kWrite); }
  bool IsAllocOnly() const { return IsAlloc() && effects_.count() == 1; }
  bool IsReadOnly() const { return IsRead() && effects_.count() == 1; }