如何使用 std::shared_ptr 的多重继承？

Question

所以，我有这样的代码：

class IUpdatable {
    virtual void onUpdate() = 0;
};
class IDrawable {
    virtual void onDraw() = 0;
};
class IEventable {
    virtual void onEvent() = 0;
};

class IObject {};
class Button : public IObject, public IUpdatable, public IDrawable, public IEventable {/*override of virtual metothods*/};
class NonVisibleButton : public IObject, public IUpdatable, public IEventable {/*override of virtual methods*/}

int main(){
    std::vector <std::shared_ptr <IObject>> buttons = {
        new Button(),
        new NonVisibleButton()
    };
    std::vector <std::weak_ptr <IEventable>> eventables = {
        buttons.at(0),
        buttons.at(1)
    };
    std::vector <std::weak_ptr <IDrawble>> drawbles = {
        buttons.at(0)
    };
}

那么，我可以实现这一点吗？如何实现？我想使用不同容器中的按钮定期更新矢量。（更准确地说，我有单独的线程来更新 IEventable 的子 class' 对象，并且从 IEventable 继承的所有东西都在这里）

Answer 1

类似这样的方法可行：

#include <vector>
#include <memory>

class IUpdatable {
public:
    virtual void onUpdate() = 0;
};
class IDrawable {
public:
    virtual void onDraw() = 0;
};
class IEventable {
public:
    virtual void onEvent() = 0;
};

class IObject {
public:
    virtual ~IObject() = default;
};

class Button : public IObject, public IUpdatable, public IDrawable, public IEventable {
public:
    void onUpdate() override {}
    void onDraw() override {}
    void onEvent() override {}
};

class NonVisibleButton : public IObject, public IUpdatable, public IEventable {
public:
    void onUpdate() override {}
    void onEvent() override {}
};

int main(){
    std::vector <std::shared_ptr <IObject>> buttons = {
        std::static_pointer_cast<IObject>(std::make_shared<Button>()),
        std::static_pointer_cast<IObject>(std::make_shared<NonVisibleButton>())
    };
    std::vector <std::weak_ptr <IEventable>> eventables = {
        std::dynamic_pointer_cast<IEventable>(buttons.at(0)),
        std::dynamic_pointer_cast<IEventable>(buttons.at(1))
    };
    std::vector <std::weak_ptr <IDrawable>> drawbles = {
        std::dynamic_pointer_cast<IDrawable>(buttons.at(0))
    };
}

老实说，我不会尝试将 Java 代码结构（接口、继承等）塞进 C++ 中...如果可能，请尝试 composition over inheritance。

Answer 2

使用局部变量来保存 Button 和 NonVisibleButton。这样做的额外好处是不需要 buttons.at 来引用它们。

int main(){
    auto b = std::make_shared<Button>();
    auto nvb = std::make_shared<NonVisibleButton>();
    std::vector <std::shared_ptr <IObject>> buttons = {
        b,
        nvb
    };
    std::vector <std::weak_ptr <IEventable>> eventables = {
        b,
        nvb
    };
    std::vector <std::weak_ptr <IDrawble>> drawbles = {
        b
    };
}

如何使用 std::shared_ptr 的多重继承？

How to use multi-inheritence with std::shared_ptr?

c++

stl

shared-ptr