text: #pragma once
  
  /// Multiple Boolean values. That is, two Boolean values: can it be true, can it be false.
  struct BoolMask
  {
      bool can_be_true = false;
      bool can_be_false = false;
  
      BoolMask() {}
      BoolMask(bool can_be_true_, bool can_be_false_) : can_be_true(can_be_true_), can_be_false(can_be_false_) {}
  
      BoolMask operator &(const BoolMask & m)
      {
          return BoolMask(can_be_true && m.can_be_true, can_be_false || m.can_be_false);
      }
      BoolMask operator |(const BoolMask & m)
      {
          return BoolMask(can_be_true || m.can_be_true, can_be_false && m.can_be_false);
      }
      BoolMask operator !()
      {
          return BoolMask(can_be_false, can_be_true);
      }
  
      /// If mask is (true, true), then it can no longer change under operation |.
      /// We use this condition to early-exit KeyConditions::check{InRange,After} methods.
      bool isComplete() const
      {
          return can_be_false && can_be_true;
      }
  
      /// These special constants are used to implement KeyCondition::mayBeTrue{InRange,After} via KeyCondition::check{InRange,After}.
      /// When used as an initial_mask argument in KeyCondition::check{InRange,After} methods, they effectively prevent
      /// calculation of discarded BoolMask component as it is already set to true.
      static const BoolMask consider_only_can_be_true;
      static const BoolMask consider_only_can_be_false;
  };
  