设计模式：享元模式（C++实现）

享元模式（Flyweight Pattern）是一种结构设计模式，它通过共享对象来有效地支持大量细粒度的对象。享元模式的目标是尽量减少内存使用，通过共享相同的数据来减少对象的数量。
以下是一个简单的C++享元模式的示例：

#include 
#include 

// 抽象享元类
class Flyweight
{
public:
    virtual void operation() = 0;
};

// 具体享元类
class ConcreteFlyweight : public Flyweight
{
private:
    std::string intrinsicState;

public:
    ConcreteFlyweight(const std::string &intrinsicState) : intrinsicState(intrinsicState) {}
    void operation() override
    {
        std::cout << "Concrete Flyweight: " << intrinsicState << std::endl;
    }
};

// 享元工厂类
class FlyweightFactory
{
private:
    std::unordered_map<std::string, Flyweight *> flyweights;

public:
    Flyweight *getFlyweight(const std::string &intrinsicState)
    {
        if (flyweights.find(intrinsicState) == flyweights.end())
        {
            flyweights[intrinsicState] = new ConcreteFlyweight(intrinsicState);
        }
        return flyweights[intrinsicState];
    }
    ~FlyweightFactory()
    {
        for (auto it = flyweights.begin(); it != flyweights.end(); ++it)
        {
            delete it->second;
        }
        flyweights.clear();
    }
};

int main()
{
    FlyweightFactory flyweightFactory;
    Flyweight *flyweight1 = flyweightFactory.getFlyweight("state1");
    Flyweight *flyweight2 = flyweightFactory.getFlyweight("state2");
    Flyweight *flyweight3 = flyweightFactory.getFlyweight("state2");
    flyweight1->operation();
    flyweight2->operation();
    flyweight3->operation();
    return 0;
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60

运行结果：

Concrete Flyweight: state1
Concrete Flyweight: state2
Concrete Flyweight: state2
1
2
3

在上述示例中，Flyweight是抽象享元类，定义了享元对象的接口。ConcreteFlyweight是具体享元类，实现了具体的享元对象。FlyweightFactory是享元工厂类，负责创建和管理享元对象。
在main()函数中，首先创建了一个享元工厂对象flyweightFactory。然后通过调用getFlyweight()方法来获取享元对象。如果工厂中不存在对应的享元对象，则创建一个新的享元对象并将其存储在工厂中；如果已存在对应的享元对象，则直接返回该对象。最后，通过调用享元对象的operation()方法来执行操作。
通过享元模式，可以减少对象的数量，节省内存空间。相同的数据可以被多个对象共享，从而降低了系统的开销。享元模式适用于需要创建大量相似对象的场景，可以提高系统的性能和效率。