Chain of Responsibility

Chain of Responsibility
目的在將一個訊息傳遞下去
讓每個物件都判斷是否有該處理的事情
就像老闆交代一件事情下來，所有員工都問問看，有沒有人會
java awt就是使用這個pattern
有點像linked-list

#define ART   0
#define ENGINEERING 1
#define SCIENCE  2
#define LABOR  3
#define POLITICS 4

class Request {
public:
 int request_type;
 Request(){}
 Request(int type)
 {
  request_type = type;
 }
};

class Handler {
public:
 int handler_type;
 Handler* next_handler;

 Handler()
 {
  this->next_handler = NULL;
 }

 void try_handle(Request* request) {
  cout << "review request...\n";
  if( request->request_type == this->handler_type ) {
   this->handle(request);
  }
  if( this->next_handler != NULL ) {
   this->next_handler->try_handle(request);
  }
 }

 void set_next_handler(Handler* next_handler)
 {
  this->next_handler = next_handler;
 }

 virtual void handle(Request* request) {

 }

};

class DirtyRequest : public Request {
public:
 DirtyRequest() : Request(POLITICS)  // 這邊算是trick, invoke superclass的constructor必須在code block外面
 {}
};

class Engineer : public Handler {
public:
 Engineer()
 {
  this->handler_type = ENGINEERING;
 }
 
 virtual void handle(Request* request) {
  cout << "Engineer Soloved\n";
 }
 
};

class Artist : public Handler {
public:
 Artist()
 {
  this->handler_type = ART;
 }
 
 virtual void handle(Request* request) {
  cout << "Artist Soloved\n";
 }
};

class Politican : public Handler {
public:
 Politican()
 {
  this->handler_type = POLITICS;
 }
 
 virtual void handle(Request* request) {
  cout << "Politican Soloved\n";
 }
};

int main()
{
 Engineer *eng = new Engineer();
 Artist *art = new Artist();
 art->set_next_handler(eng);
 Politican *pol = new Politican(); 
 pol->set_next_handler(art);
 pol->try_handle( new DirtyRequest() );
 
 return 0;
}