flyweight.cpp

#include <map>
#include <iostream>

// "Flyweight"
class Character
{
public:
    virtual ~Character() {}
    virtual void display() const = 0;

protected:
    char mSymbol;
    int  mWidth;
    int  mHeight;
    int  mAscent;
    int  mDescent;
    int  mPointSize;
};

// "ConcreteFlyweight"
class ConcreteCharacter : public Character
{
public:
    // Constructor
    ConcreteCharacter( char aSymbol, int aPointSize )
    {
        mSymbol = aSymbol;
        mWidth = 120;
        mHeight = 100;
        mAscent = 70;
        mDescent = 0;
        mPointSize = aPointSize;
    }

    // from Character
    virtual void display() const {
        std::cout << mSymbol << " ( PointSize " << mPointSize << " )\n";
    }
};


// "FlyweightFactory"
template < int POINT_SIZE = 10 >
class CharacterFactory
{
public:
    const Character& getCharacter( char aKey )
    {
        // Uses "lazy initialization"
        Characters::const_iterator it = mCharacters.find( aKey );
        if ( mCharacters.end() == it ) {
            const Character* character = new ConcreteCharacter(aKey, POINT_SIZE);
            mCharacters[aKey] = character;
            return *character;
        } else {
            return *it->second;
        }
    }

    virtual ~CharacterFactory(){
        for (Characters::const_iterator it = mCharacters.begin(); it != mCharacters.end(); ++it)
             delete it->second;
        }

private:
    typedef std::map < char, const Character* > Characters;
    Characters mCharacters;
};


int main(){
    std::string document = "AAZZBBZB";

    CharacterFactory<12> characterFactory;

    for (std::string::const_iterator it = document.begin(); it != document.end(); ++it){
        const Character& character = characterFactory.getCharacter( *it );
        character.display();
    }
    return 0;
}