delegate vs policy

1. delegate

 

class HelloWord {public:struct InputDelegate {virtual void BuildGround() = 0;};struct OutputDelegate {virtual void BuildWall() = 0;};virtual void Run(InputDelegate* in, OutputDelegate* out);};class DirectInput: public HelloWorld::InputDelegate {public:virtual void BuildGround() { cout << "DirectInput" << endl; }}class DirectOutput: public HelloWorld::OutputDelegate {public:virtual void BuildWall() { cout << "DirectOutput" << endl; }}class DirectRun {public:DirectRun() {hello_ = new HelloWorld;}void Run() {DirectInput* in = new DirectInput;DirectOutput* out = new DirectOutput;hello_->Run(in, out);}private:HelloWorld* hello_;} 

如果要从文件输入，可定义一个 class FileInput: public HelloWorld::InputDelegate;

 

2. policy

 

template <class Host>class AspectDirectInput {public:void Input() {}};template <class Host>class AspectDierctOutput [public:void Output() {}};class HelloWorld: public AspectDirectInput, public AspectDirectOutput {void Run() {Input(); // from AspectDirectInputOutput(); // from AspectDirectOutput}} 

如果要定义从文件获得输入，可写个AspectFileInput类即可

 

policy 那是相当优雅啊。