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 patternYu Chen &Ider ZhengCSE 776 - Design Patterns by Jim FawcettFall 2011

2. Who?What? Why? When?How?4W1HY & IStructure/ParticipantsConsequencesApplicabilityImplementation

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

4. Real life analogyCopy Machine

5. Real life analogyCopy MachineProduct PrototypesDie Sinking

6. structure

7. structurePrototypeConcreteConcreteClientClone()Clone()Clone()Operation()p = prototype->Clone()Return copy of itselfReturn copy of itself

8. participantsPrototypeDeclares an instance for cloning itselfConcrete PrototypeImplement an operation of cloning itselfClientCreates an object by asking the prototype to clone itself

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

11. Implementation issuesImplementing the Clone operation.Binding the concrete prototypes

12. Copy Constructor VSPrototype Pattern

13. Shallow CopyVSDeep Copy

14. Implementation issuesImplementing the Clone operation.Binding the concrete prototypes

15. structure?PrototypeConcreteConcreteClientClone()Clone()Clone()Operation()p = prototype->Clone()Return copy of itselfReturn copy of itself

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

17. Prototype managersCreate and destroy prototype at run-timeRegister new prototypesUnregister prototypesClient retrieve and store prototype from prototype managerUse map<key,prototype>

18. CASE STUDY - tetris

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