树突变和共享指针问题的访问者模式

#include <iostream>
#include <vector>
#include <memory>

// 元素接口
class Element {
public:
    virtual void accept(class Visitor* visitor) = 0;
};

// 具体元素A
class ConcreteElementA : public Element {
public:
    void accept(Visitor* visitor) override {
        visitor->visit(this);
    }
    void operationA() {
        std::cout << "ConcreteElementA operation" << std::endl;
    }
};

// 具体元素B
class ConcreteElementB : public Element {
public:
    void accept(Visitor* visitor) override {
        visitor->visit(this);
    }
    void operationB() {
        std::cout << "ConcreteElementB operation" << std::endl;
    }
};

// 访问者接口
class Visitor {
public:
    virtual void visit(ConcreteElementA* element) = 0;
    virtual void visit(ConcreteElementB* element) = 0;
};

// 具体访问者
class ConcreteVisitor : public Visitor {
public:
    void visit(ConcreteElementA* element) override {
        element->operationA();
    }
    void visit(ConcreteElementB* element) override {
        element->operationB();
    }
};

int main() {
    std::vector<std::shared_ptr<Element>> elements;
    elements.push_back(std::make_shared<ConcreteElementA>());
    elements.push_back(std::make_shared<ConcreteElementB>());

    ConcreteVisitor visitor;
    for (auto& element : elements) {
        element->accept(&visitor);
    }

    return 0;
}