The prototype pattern specifies the kinds of objects to create using a prototypical instance, and creates new objects by copying this prototype. It allows objects to be cloned without knowing their concrete classes. The prototype declares a cloning method that returns a copy of itself. A client creates an object by asking the prototype to clone itself. This pattern avoids subclassing and allows object types to vary at runtime. It is useful when object creation depends on runtime parameters or when classes have a small number of derived forms.

1. Prototype pattern Yu Chen &Ider Zheng CSE 776 - Design Patterns by Jim Fawcett Fall 2011

2. Who? What? Why? When? How? 4W1H Y & I Structure/Participants Consequences Applicability Implementation

3. Intent “Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype.”

4. Real life analogy Copy Machine

5. Real life analogy Copy Machine Product Prototypes Die Sinking

6. structure

7. structure Prototype Concrete Concrete Client Clone() Clone() Clone() Operation() p = prototype->Clone() Return copy of itself Return copy of itself

8. participants Prototype Declares an instance for cloning itself Concrete Prototype Implement an operation of cloning itself Client Creates an object by asking the prototype to clone itself

9. consequences Specifying new objects by varying values. Specifying new objects by varying structure. Reduced subclassing. Configuring an application with classes dynamically. Adding and removing products at run-time.

10. applicability When a system should be independent of how its products are created, composed, and represented. When the classes to instantiate are specified at run-time To avoid building a class hierarchy of factories that parallels the class hierarchy of products When instances of a class can have one of only a few different combinations of state.

11. Implementation issues Implementing the Clone operation. Binding the concrete prototypes

12. Copy Constructor VS Prototype Pattern

13. Shallow Copy VS Deep Copy

14. Implementation issues Implementing the Clone operation. Binding the concrete prototypes

15. structure ? Prototype Concrete Concrete Client Clone() Clone() Clone() Operation() p = prototype->Clone() Return copy of itself Return copy of itself

16. Factories Factory: private ConcreteA* _prototypeA; // we can have more Factory: public MakeA() { return _prototypeA->clone(); } Client: Base* obj = MakeA(); Client: obj->MoreActions();

17. Prototype managers Create and destroy prototype at run-time Register new prototypes Unregister prototypes Client retrieve and store prototype from prototype manager Use map<key,prototype>

18. CASE STUDY - tetris

19. Tetris cont.

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23. Tetris Cont.

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27. One more thing Thank You!