c++ - 如何从 vector 中返回给定类型的元素？

Question

我有一个类，EscapeRoomWrapper，以及从它派生的两个类，ScaryRoom 和 KidsRoom。

在另一个类 Company 中，我添加了一个指向所有房间对象的指针的 vector(EscapeRoomWrapper、ScaryRoom 和 KidsRoom)。我想在 Company 类中编写一个函数，在其中我给它一种房间类型，它应该返回所有存在于 vector 中的该类型的所有房间房间。

我想过使用typeid，但是教授禁止我们使用它。我最后的想法是使用 dynamic_cast。

typedef enum{
    SCARY_ROOM, KIDS_ROOM, BASE_ROOM
}RoomType;

class Company{
    string CompanyName;
    std::vector<EscapeRoomWrapper*> Rooms;

public:
    std::vector<EscapeRoomWrapper*>& getAllRoomsByType(RoomType type) const;
};

class EscapeRoomWrapper{
    EscapeRoom room;
    std::vector<Enigma> Enigmas;
public:
    // functions here
};

class ScaryRoom : public EscapeRoomWrapper {
private:
    int ageLimit;
    int NumOfScaryEnigmas;
public:
    // functions for escary room
};

class KidsRoom : public EscapeRoomWrapper {
private:
    int ageLimit;
public:
    // functions for kidsroom
};

关于如何实现此功能的任何想法？

std::vector<EscapeRoomWrapper*>& getAllRoomsByType(RoomType type) const

Answer 1

认为可以使用 dynamic_cast 是正确的，例如:

class Company {
    ...
    std::vector<EscapeRoomWrapper*> Rooms;
public:
    std::vector<EscapeRoomWrapper*> getAllRoomsByType(RoomType type) const;
};

std::vector<EscapeRoomWrapper*> Company::getAllRoomsByType(RoomType type) const
{
    std::vector<EscapeRoomWrapper*> result;

    switch (type) {
        case SCARY_ROOM:
            for (size_t i = 0; i < Rooms.size(); ++i) {
                if (dynamic_cast<ScaryRoom*>(Rooms[i])) {
                    result.push_back(Rooms[i]);
                }
            } 
            break;

        case KIDS_ROOM:
            for (size_t i = 0; i < Rooms.size(); ++i) {
                if (dynamic_cast<KidsRoom*>(Rooms[i])) {
                    result.push_back(Rooms[i]);
                }
            } 
            break;

        case BASE_ROOM:
            result = Rooms;
            break;
    }

    return result;
}

但是，dynamic_cast 有一些运行时开销，它取决于为类生成 RTTI 的编译器(默认情况下会这样做，但可以 禁用)。还有其他可用的解决方案。

您可以定义一个虚函数让每个类从 enum 报告其类型，然后您可以查看这些类型值:

class EscapeRoomWrapper {
    ...
public:
    ...
    virtual RoomType getRoomType() const { return BASE_ROOM; }
};

class ScaryRoom : public EscapeRoomWrapper {
    ... 
public:
    ...
    RoomType getRoomType() const { return SCARY_ROOM; }
};

class KidsRoom : public EscapeRoomWrapper {
    ... 
public:
    ...
    RoomType getRoomType() const { return KIDS_ROOM; }
};

std::vector<EscapeRoomWrapper*> Company::getAllRoomsByType(RoomType type) const
{
    std::vector<EscapeRoomWrapper*> result;

    for (size_t i = 0; i < Rooms.size(); ++i) {
        if ((Rooms[i]->getRoomType() == type) || (type == BASE_ROOM)) {
            result.push_back(Rooms[i]);
        }
    }

    return result;
}

或者，您可以只为每种房间类型存储单独的列表:

class Company {
    ...
    std::vector<EscapeRoomWrapper*> ScaryRooms;
    std::vector<EscapeRoomWrapper*> KidsRooms;
    std::vector<EscapeRoomWrapper*> AllRooms;
public:
    std::vector<EscapeRoomWrapper*> getAllRoomsByType(RoomType type) const;
};

std::vector<EscapeRoomWrapper*> Company::getAllRoomsByType(RoomType type) const
{
    switch (type) {
        case SCARY_ROOM:
            return ScaryRooms;

        case KIDS_ROOM:
            return KidsRooms;

        case BASE_ROOM:
            return AllRooms;
    }

    return std::vector<EscapeRoomWrapper*>();
}