享元模式

#include <string>
#include <map>
using namespace std;
class Font {
private:
    //unique object key
    string key;
    //object state
    //....
public:
    Font(const string& key) {
        //...
    }
};
class FontFactory 
{
private:
    map<string, Font* > fontPool;
public:
    Font* GetFont(const string& key) {
        map<string, Font*>::iterator item = fontPool.find(key);
        if (item != fontPool.end()) {
            return fontPool[key];
        }
        else {
            Font* font = new Font(key);
            fontPool[key] = font;
            return font;
        }
    }
    void clear() {
        //...
    }
};