1. Practices of Good Component Design Microsoft Research Asia Advanced Technology

2. 2 Introduction Barn-Wan Li Born in Toronto, Canada B.A., University of California, Berkeley Microsoft Silicon Valley Campus Microsoft Research Asia, Beijing

3. 3 Software Components Conceptualized in the 60s Improve encapsulation and reuse

4. 4 Software Components Conceptualized in the 60s Improve encapsulation and reuse

5. 5 Software Components Conceptualized in the 60s Improve encapsulation and reuse PowerPointWordExcel OfficeArt Drawing

6. 6 How is a Component different than an Object? Object-oriented Programming History –created in the 60s real-world modeling and metaphors microcosm of objects with messages

7. 7 How is a Component different than an Object? Object-oriented Programming History –created in the 60s real-world modeling and metaphors microcosm of objects with messages –the promise of the 80s combining the concept of components for abstraction and reuse

8. 8 How is a Component different than an Object? Object-oriented Programming History –created in the 60s real-world modeling and metaphors microcosm of objects with messages –the promise of the 80s combining the concept of components for abstraction and reuse –fear in the 90s fragile software reuse with objects

9. 9 Inheritance for Reuse class Car { };

10. 10 Inheritance for Reuse class Car { };

11. 11 Inheritance for Reuse class Car { }; class Racecar : public Car { }; class Truck : public Car { }; class Taxi : public Car { };

12. 12 Inheritance for Reuse class Truck { };

13. 13 Inheritance for Reuse class Truck { }; class FireHydrant { }; class FireTruck : public Truck, public FireHydrant { };

14. 14 Inheritance for Reuse class Truck { }; class FireHydrant { }; class FireTruck : public Truck, public FireHydrant { };

15. 15 Inheritance for Reuse polymorphism incremental behavior changes self-recursive down-calls

16. 16 Inheritance for Reuse polymorphism incremental behavior changes self-recursive down-calls class Car { void Stop() { SayMessage(); } virtual void SayMessage() { cout << “Bye!” << endl; } }; class Taxi : public Car { virtual void SayMessage() { cout << “50 RMB please” << endl; } };

17. 17 Inheritance for Reuse

18. 18 Inheritance for Reuse

19. 19 Inheritance for Reuse breaks encapsulation breaks data hiding breaks implementation hiding compile-time and run- time dependencies syntactic and semantic fragility

20. 20 Reuse and Sharing - Templates class LinkList { … }; class MyObjList : public LinkList { … };

21. 21 Reuse and Sharing - Templates template class LinkList { … T *operator -> () { return &m_t; } T m_t; }; class MyObj { … }; typedef LinkList MyObjList; class LinkList { … }; class MyObjList : public LinkList { … };

22. 22 Reuse and Sharing - Templates class LinkList { … }; class MyObjList : public LinkList { … }; class MyObjTree : public BinTree { … }; template class LinkList { … T *operator -> () { return &m_t; } T m_t; }; class MyObj { … }; typedef LinkList MyObjList; typedef BinTree MyObjTree;

23. 23 Reuse and Sharing - Templates class LinkList { }; class MyObjList : public LinkList { }; class MyObjTree : public BinTree { }; class MyObjList : public MyObj, public LinkList { }; template class LinkList { … T *operator -> () { return &m_t; } T m_t; }; class MyObj { … }; typedef LinkList MyObjList; typedef BinTree MyObjTree;

24. 24 class LinkList { }; class MyObjList : public LinkList { }; class MyObjTree : public BinTree { }; class MyObjList : public MyObj, public LinkList { }; template class LinkList { … T *operator -> () { return &m_t; } T m_t; }; class MyObj { … }; typedef LinkList MyObjList; typedef BinTree MyObjTree; Reuse and Sharing - Templates

25. 25 Reuse and Sharing - Containment class LinkList { … void Set(Object *pobj) { m_pObject = pobj; } Object *Get() { return m_pObject; } Object *m_pObject; }; class Object { … Object() { m_linklist.Set(pobj); } Object *Next() { return m_linklist.Next().Get(); } … LinkList m_listlist; };

26. 26 What is a Component different layers –within a single system –sharable library –crossing application boundaries –crossing system boundaries encapsulation and abstraction

27. 27 How is a Component Design “Good”? the component’s interface upholds a clear “contract”. changes to the implementation of the component do not require changes in the code that uses it. the component has reuse value when the time required to understand and integrate for a new user is faster and easier than to rewrite it.

28. 28 Life-time of a Component conception of an abstract layer, a sharable service, or a piece of code that has reuse value understanding the requirements and limitations designing the interfaces implementation creating the user of the component that wraps and tests the implementation

29. 29 Example – Face Detection BOOL DetectFace(HBITMAP image, CArray &faces, CArray &angles);

30. 30 Example – Face Detection BOOL DetectFace(HBITMAP image, CArray &faces, CArray &angles); BOOL DetectFace(HBITMAP image, int &facenum, RECT *faces[], long *angles[]);

31. 31 Example – Face Detection BOOL DetectFace(HBITMAP image, CArray &faces, CArray &angles); BOOL DetectFace(HBITMAP image, int &facenum, RECT *faces[], long *angles[]); ULONG DetectFaceNumber(HBITMAP image); BOOL DetectFace(HBITMAP image, int index, RECT *face, long *angle);

32. 32 Example – Face Detection BOOL DetectFace(HBITMAP image, CArray &faces, CArray &angles); BOOL DetectFace(HBITMAP image, int &facenum, RECT *faces[], long *angles[]); ULONG DetectFaceNumber(HBITMAP image); BOOL DetectFace(HBITMAP image, int index, RECT *face, long *angle); BOOL DetectFace(HDC image, int width, int height, int index, RECT *face, long *angle); BOOL DetectFace(void pvBits, int width, int height, int bitsperpixel, int index, RECT *face, long *angle);

33. 33 Introducing COM Component Object Model interface == pure virtual class may be more than one object language independent interface IUnknown { ULONG AddRef(); // reference counting ULONG Release(); HRESULT QueryInterface(); // dynamic casting }

34. 34 Face Detection Interface interface IFaceDetector { HRESULT Detect(IFDImage *pImage, IFDFaceEnum **ppFaces); };

35. 35 Face Detection Interface interface IFaceDetector { HRESULT Detect(IFDImage *pImage, IFDFaceEnum **ppFaces); }; interface IFDImage { HRESULT SetHBitmap(HBITMAP bitmap); HRESULT SetHDC(HDC image, int width, int height); HRESULT SetBits(void pvBits, int width, int height, int bitsperpixel); };

36. 36 Face Detection Interface interface IFaceDetector { HRESULT Detect(IFDImage *pImage, IFDFaceEnum **ppFaces); }; interface IFDImage { HRESULT SetHBitmap(HBITMAP bitmap); HRESULT SetHDC(HDC image, int width, int height); HRESULT SetBits(void pvBits, int width, int height, int bitsperpixel); }; interface IFDFaceEnum { HRESULT GetNum(ULONG *pNum); HRESULT GetFace(int index, IFDFace **pFace); };

37. 37 Face Detection Interface interface IFaceDetector { HRESULT Detect(IFDImage *pImage, IFDFaceEnum **ppFaces); }; interface IFDImage { HRESULT SetHBitmap(HBITMAP bitmap); HRESULT SetHDC(HDC image, int width, int height); HRESULT SetBits(void pvBits, int width, int height, int bitsperpixel); }; interface IFDFaceEnum { HRESULT GetNum(ULONG *pNum); HRESULT GetFace(int index, IFDFace **pFace); }; interface IFDFace { HRESULT GetRect(RECT *pRect); HRESULT GetAngle(long *pAngle); };

38. 38 Face Detection Interface interface IFaceDetector { HRESULT Detect(IFDImage *pImage, IFDFaceEnum **ppFaces); }; interface IFDImage { HRESULT SetHBitmap(HBITMAP bitmap); HRESULT SetHDC(HDC image, int width, int height); HRESULT SetBits(void pvBits, int width, int height, int bitsperpixel); }; interface IFDFaceEnum { HRESULT GetNum(ULONG *pNum); HRESULT GetFace(int index, IFDFace **pFace); }; interface IFDFace { HRESULT GetRect(RECT *pRect); HRESULT GetAngle(long *pAngle); HRESULT GetLeftEye(RECT *pRect); HRESULT GetRightEye(RECT *pRect); HRESULT GetAccuracy(long *pPercent); };

39. 39 Face Detection Interface Face Detection Component Application

40. 40 Face Detection Interface IFaceDetectorIFDImage Face Detection Component IFDFaceEnumIFDFace Application

41. 41 Face Detection Implementation interface IFaceDetector { HRESULT Detect(IFDImage *pImage, IFDFaceEnum **ppFaces); };

42. 42 Face Detection Implementation interface IFaceDetector { HRESULT Detect(IFDImage *pImage, IFDFaceEnum **ppFaces); }; class CFaceDetector : public IFaceDetector { HRESULT Detect(IFDImage *pImage, IFDFaceEnum **ppFaces); };

43. 43 Face Detection Implementation HRESULT CFaceDetector::Detect(IFDImage *pImage, IFDFaceEnum **ppFaces) { if (pImage == NULL || ppResult == NULL) return E_INVALIDARG; : * ppFaces = new CFDFaceEnum; return E_SUCCESS; } interface IFaceDetector { HRESULT Detect(IFDImage *pImage, IFDFaceEnum **ppFaces); }; class CFaceDetector : public IFaceDetector { HRESULT Detect(IFDImage *pImage, IFDFaceEnum **ppFaces); };

44. 44 Face Detection Usage void main() { CComPtr pDetector; pDetector.CreateInstance( CLSID_FaceDetector); : CComPtr pResult; pDetector->Detect(pImage, pResult); : } interface IFaceDetector { HRESULT Detect(IFDImage *pImage, IFDFaceEnum **ppFaces); }; class CFaceDetector : public IFaceDetector { HRESULT Detect(IFDImage *pImage, IFDFaceEnum **ppFaces); };

45. 45 Face Detection Interface IFaceDetector CFaceDetector IFDImage Face Detection Component IFDFaceEnum CFDFaceEnum IFDFace CFDFace Application

46. 46 Tips for Authoring a Component know your callers check for parameter errors at external APIs, assert for internal avoid allocating memory that the caller must free use existing types-- or create your own abstract interfaces aggregate types for reuse or to hide complexity

47. 47