状态模式（C++）

定义：状态模式（State Pattern）是一种行为设计模式，它允许对象在内部状态改变时改变它的行为，对象看起来似乎修改了它的类。状态模式将状态相关的行为封装到单独的类中，并将这些对象组合成状态模式，允许状态对象在运行时改变行为。

        代码：

class TicketMachine;
// 状态接口
class State {
public:
    virtual ~State() = default;
    virtual void handle(std::shared_ptr<TicketMachine> machine) = 0;
    virtual std::string getStateName() const = 0;
};

// 上下文：售票机
class TicketMachine : public std::enable_shared_from_this<TicketMachine> {
public:
    TicketMachine() {}

    void insertMoney() {
        std::cout << "Money inserted." << std::endl;
        handle();
    }

    void setState(std::shared_ptr<State> newState) {
        state = newState;
        std::cout << "State changed to: " << state->getStateName() << std::endl;
    }

    std::string getCurrentState() const {
        return state->getStateName();
    }

private:
    void handle() {
        state->handle(shared_from_this());
    }

    std::shared_ptr<State> state;
};

// 具体状态：票已售罄
class SoldOutState : public State {
public:
    void handle(std::shared_ptr<TicketMachine> machine) override {
        std::cout << "Sorry, tickets are sold out." << std::endl;
    }
    std::string getStateName() const override {
        return "SoldOut";
    }
};

// 具体状态：可以售票
class AvailableState : public State {
public:
    void handle(std::shared_ptr<TicketMachine> machine) override {
        std::cout << "Ticket is available. Selling one ticket." << std::endl;
        machine->setState(std::make_shared<SoldOutState>()); // 改变状态
    }
    std::string getStateName() const override {
        return "Available";
    }
};

int main() {
    auto machine = std::make_shared<TicketMachine>();
    machine->setState(std::make_shared<AvailableState>());

    machine->insertMoney(); // Ticket is available. Selling one ticket. State changed to: SoldOut
    machine->insertMoney(); // Sorry, tickets are sold out.

    return 0;
}