设计模式（3）--对象结构(6)--享元

1. 意图

    运用共享技术有效地支持大量细粒度的对象。

2. 三种角色

    抽象享元(Flyweight)、具体享元(Concrete Flyweight)、具体不共享元(UnShared Concrete Flyweight)、享元工厂(Flyweight Factory)

3. 优点

    3.1 节省空间，共享越多，节省越大

4. 缺点

    4.1 增加了运行时开销 

5. 相关模式 

    5.1 享元模式通常和组合模式结合，用共享叶节点的有向无环图实现一个逻辑上的层次结构

    5.2 通常，最好用享元实现State和Strategy对象。 

6. 代码示意(C++)

#pragma once
#include 
#include 
#include 

#include "Flyweight.h"
int main() {
	FlyweightFactory* pFactory = new FlyweightFactory();
	Flyweight* pFlyweight = pFactory->GetFlyweight("shared");
	if (0 != pFlyweight) {
		pFlyweight->operation(0);
	}
	pFlyweight = pFactory->GetFlyweight("shared");
	if (0 != pFlyweight) {
		pFlyweight->operation(1);
	}

	pFlyweight = pFactory->GetFlyweight("unshared");
	if (0 == pFlyweight) {
		pFlyweight = pFactory->GetUnsharedFlyweight();
		pFlyweight->operation(1);
		delete pFlyweight;
	}

	delete pFactory;
	return 0;
}

运行结果：

6.1 第二次使用SharedFlyweight时从map里取出，而不需要重新创建(3.1)

6.2 Flyweight不强制共享，比如UnsharedFlyweight