C + + design mode shallow to enjoy meta-mode

Enjoy meta mode (Flyweight): Use sharing technology to effectively support a large number of fine-grained objects.

Four role classes:

Flyweight: The superclass or interface of all the specific classes of the class, through which the flyweight can accept and act on the external state.

Flyweight to enjoy meta-factory class: An exclusive meta factory that is used to create and manage flyweight, when a user requests a flyweight, the Flyweightfactory object provides a created instance or creates one if it does not exist.

Concreteflyweight: Inherit flyweight superclass or implement flyweight interface, and increase storage space for internal state.

Unsharedconcreteflyweight specific flyweight subclasses that do not need to be shared, refer to flyweight subclasses that do not require sharing. Because flyweight interface class sharing is possible, it does not force a share.

Pattern implementation:

[code]//class Flyweight{public:    virtual void operation (int extrinsicstate) {}};//-specific classes class Concreteflyweight : Public flyweight{public:    virtual void operation (int extrinsicstate) override{        std::cout << " Concreteflyweight: "<< extrinsicstate << Std::endl;    }};/ /Flyweight Subclass Class Unsharedconcreteflyweight:public Flyweight{public:    virtual void operation (int Extrinsicstate) {        std::cout << "unsharedconcreteflyweight:" << extrinsicstate << Std::endl;    }}; Enjoy meta factory, used to create and manage Flyweight objects class Flyweightfactory{private:    std::map<std::string, flyweight*> flyweights; Public:    flyweightfactory () {        flyweights["X"] = new Concreteflyweight;        flyweights["Y"] = new Concreteflyweight;        flyweights["Z"] = new Concreteflyweight;    }    flyweight* getflyweight (std::string key) {        return (flyweight*) Flyweights[key];}    ;

Client:

[Code]//clientint Main () {    //external state    int extrinsicstate =;    Factory    flyweightfactory *f = new Flyweightfactory;    flyweight* FX = f->getflyweight ("X");    Fx->operation (--extrinsicstate);  output:concreteflyweight:21    flyweight* fy = f->getflyweight ("Y");    Fy->operation (--extrinsicstate);  Output:concreteflyweight:20    flyweight* FZ = f->getflyweight ("Z");    Fz->operation (--extrinsicstate);  output:concreteflyweight:19    Flyweight *uf = new Unsharedconcreteflyweight;  Output:unsharedconcreteflyweight:18    uf->operation (--extrinsicstate);    return 0;}

Enjoy meta-mode benefits:

If an application uses a large number of objects, and a large number of these objects cause significant storage overhead, you should consider using them.

Most states of an object can use an external state, and if you delete an object's external state, you can replace many group objects with a relatively small number of shared objects, and you can consider using the enjoy meta mode.

The above is the C + + design mode to enjoy the meta-mode of content, more relevant content please pay attention to topic.alibabacloud.com (www.php.cn)!

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