帐前卒专栏

Without software, we are nothing.

Design Pattern CHAIN of Reponsibility

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#include<cstdio>

using namespace std;
namespace pattern{
  /// this pattern links all handler as a line, if previous handler can process a request, it wil not be
  /// send to next handler. For example, if someone requested changing programming style, 
  /// this decision will be made by a programmer. 
  /// He will change his programming style without noticing his lead. 
  /// But if someone request changing the requirements, the programmer can not make this decision. 
  /// He will noticing his lead, and make his lead decided.

  /// this is request class.
  #define STYLE 0
  #define REQIREMENT 1
  class Request{
      public:
          int type; // changing programming style or changing requirements?

  };

  /// this class for processing request.
  class Handler{
  private:
      Handler* parent;
  public:
      Handler(Handler* p):parent(p){}
      virtual bool DoHandle(Request& r)=0;
      void Process(Request& r);
      virtual ~Handler(){}
  };

  void Handler::Process(Request& r){
      if(!this->DoHandle(r) && NULL != parent){
          parent->Process(r);
      }
  }

  class Programmer: public Handler{
      public:
      Programmer(Handler* p):Handler(p){}
      virtual bool DoHandle(Request& r);

  };
  bool Programmer::DoHandle(Request& r){
      if(r.type == STYLE){
          printf("programmer: I can process changing programming style\n");
          return true;
      }else{
          printf("programmer: I can not process this request. I will report this to my lead!\n");
          return false;
      }

  }

  class Lead:public Handler{
      public:
      Lead(Handler* p):Handler(p){}
      virtual bool DoHandle(Request& r);

  };
  bool Lead::DoHandle(Request& r){
      if(r.type == REQIREMENT){
          printf("lead: I will process changing reqirements\n");
          return true;
      }
      return false;
  }
}

int main(){
  pattern::Lead lead((pattern::Handler*)NULL);
  pattern::Programmer programmer(&lead);
  pattern::Request r;
  r.type = STYLE;
  programmer.Process(r);
  r.type = REQIREMENT;
  programmer.Process(r);
  return 0;

}

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