设计模式之责任链Chain of Responsibility

将一种响应（请求）通过一条彼此关联的处理类处理。一般遵照由小到大的粒度。

典型的例子：界面帮助请求

代码示例：

class PurchasePower{protected:static final double _BASE = 500;PurchasePower* _successor;protected:virtual double getAllowable() = 0;virtual string getRole() = 0;void setSuccessor(PurchasePower* successor){_successor = successor;}void processRequest(PurchaseRequest* request){if(reuqest->getAmount() < getAllowable() ){cout << getRole() << "will approve $" + request->getAmount() << endl;}else if(_successor != nullptr){_successor->processRequest(request);}}};class ManagerPPower : public PurchasePower{protected:virtual double getAllowable() override{return _BASE * 10;}virtual string getRole() override{return "Manager";}};class DirectorPPower : public PurchasePower{protected:virtual double getAllowable() override{return _BASE * 20;}virtual string getRole() override{return "Director";}};class VicePresidentPPower : public PurchasePower{protected:virtual double getAllowable() override{return _BASE * 40;}virtual string getRole() override{return "Vice President";}};class PresidentPPower : public PurchasePower{protected:virtual double getAllowable() override{return _BASE * 60;}virtual string getRole() override{return "President";}};class PurchaseRequest{private:double _amount;string _purpose;public:PurchaseRequest(double amount, string purpose){_amount = amount;_purpose = purpose;}double getAmount(){return _amount;}void setAmount(double amount){_amount = amount;}string getPurpose(){return _purpose;}void setPurpose(string purpose){_purpose = purpose;}};void main(){ManagerPPower* manager = new ManagerPPower();DirectorPPower* director = new DirectorPPower();VicePresidentPPower* vp = new VicePresidentPPower();PresidentPPower* president = new PresidentPPower();manager->setSuccessor(director);director->setSuccessor(vp);vp->setSuccessor(president);try{while(true){cout << "Enter the amount to check who should approve your expenditure." << endl;cout << ">" << endl;double d = 0;cin >> d;manager->processRequest(new PurchaseRequest(d, "General"));}}catch(...){exit(1);}}