zeus

0 #include <cassert>

1 #include <iostream>

2 #include <memory>

3 #include <string>

4 #include <string_view>

5

6 class PetVisitor {

7 public:

8 virtual ~PetVisitor() = default;

9 };

10

11 class Pet {

12 std::string m_color;

13

14 public:

15 virtual ~Pet() = default;

16 Pet(std::string_view color) : m_color(color) {};

17

18 virtual void accept(PetVisitor &v) = 0;

19

20 const std::string &color() const { return m_color; }

21 };

22

23 class Cat;

24

25 class CatVisitor {

26 public:

27 virtual void visit(Cat *c) = 0;

28 };

29

30 class Cat : public Pet {

31 public:

32 using Pet::Pet;

33

34 void accept(PetVisitor &v) override {

35 if (CatVisitor *cv = dynamic_cast<CatVisitor *>(&v)) {

36 cv->visit(this);

37 } else {

38 assert(false);

39 }

40 };

41 };

42

43 class Dog;

44

45 class DogVisitor {

46 public:

47 virtual void visit(Dog *d) = 0;

48 };

49

50 class Dog : public Pet {

51 public:

52 using Pet::Pet;

53

54 void accept(PetVisitor &v) override {

55 if (DogVisitor *cv = dynamic_cast<DogVisitor *>(&v)) {

56 cv->visit(this);

57 } else {

58 assert(false);

59 }

60 };

61 };

62

63 class FeedingVisitor : public PetVisitor, public CatVisitor, public DogVisitor {

64 public:

65 void visit(Cat *c) override {

66 std::cout << "Feed tuna to the " << c->color() << " cat\n";

67 }

68

69 void visit(Dog *c) override {

70 std::cout << "Feed streak to the " << c->color() << " dog\n";

71 }

72 };

73

74 class BathingVisitor : public PetVisitor, public DogVisitor {

75 public:

76 void visit(Dog *c) override {

77 std::cout << "Wash the " << c->color() << " dog\n";

78 }

79 };

80

81 int main() {

82 std::unique_ptr<Pet> c(new Cat("orange"));

83 std::unique_ptr<Pet> d(new Dog("brown"));

84

85 FeedingVisitor fv;

86 c->accept(fv);

87 d->accept(fv);

88

89 BathingVisitor bv;

90 // c->accept(bv);

91 d->accept(bv);

92

93 return 0;

94 }