template<class T>
struct IsSetProperty
{
  IsSetProperty(): property(0),	isSetProperty(false)
  {
  }
  T property;
  bool isSetProperty;
};


class Foo
{
public:
  Foo(): property1(0), isSetProperty1(false)
  {
  }
  //getter + setters depending on the case #1 or #2
private:
  // first case using another bool to ensure that property is set.
  int property1;
  bool isSetProperty1;
  // second case using struct IsSetProperty
  IsSetProperty<int> property2;
};