C++设计模式之十一：Flyweight（享元）

一、意图：

运用共享技术有效地支持大量细粒度的对象；

二、类图：

三、组成元素：

Flyweight：接受并作用于外部状态的接口；

ConcreteFlyweight：实现Flyweight，并为内部状态提供存储空间，这个对象必须是可以共享的；

UnshareConcreteFlyweight：不可共享的对象；

FlyweightFactory：创建并管理flyweight对象；

四、实现代码：

#include <iostream> 
#include <cassert> 
#include <vector> 
#include <string> 

using namespace std; 

class Flyweight 
{ 
public: 
    virtual ~Flyweight()
	{

	} 
    virtual void Operation(const string & extrinsicState)
	{

	} 
    string GetIntrinsicState()
	{
		return this->_intrinsicState;
	} 
protected: 
    Flyweight(string intrinsicState)
	{
		this->_intrinsicState = _intrinsicState;
	} 
private: 
	//固有状态
    string _intrinsicState; 
}; 
class ConcreteFlyweight:public Flyweight 
{ 
    public: 
    ConcreteFlyweight(string intrinsicState):Flyweight(intrinsicState) 
    {cout<<"ConcreteFlyweight Build ...."<<intrinsicState<<endl;} 
    ~ConcreteFlyweight(){} 
    void Operation(const string & extrinsicState) 
    { 
        cout<<"ConcreteFlyweight:内蕴"<<this->GetIntrinsicState() 
        <<"ConcreteFlyweight:外蕴"<<extrinsicState<<endl; 
    } 
}; 
class FlyweightFactory 
{ 
    public: 
    FlyweightFactory(){} 
    ~FlyweightFactory(){} 
    Flyweight * GetFlyweight(const string &key) 
    { 
        vector<Flyweight *>::iterator it = _fly.begin(); 
        for(;it != _fly.end(); it++) 
        { 
            if( (*it)->GetIntrinsicState() == key) 
                cout<<"already created by users..."<<endl; 
            return *it; 
        } 
        Flyweight *fn = new ConcreteFlyweight(key); 
        _fly.push_back(fn); 
        return fn;   
    } 
    private: 
		vector<Flyweight*> _fly; 
}; 
void main() 
{ 
    FlyweightFactory *fc = new FlyweightFactory(); 
    Flyweight * fw1 = fc->GetFlyweight("hello"); 
    Flyweight * fw2 = fc->GetFlyweight("world!"); 
    Flyweight * fw3 = fc->GetFlyweight("hello"); 
}