Visitor - 访问者模式

class Equipment
{
public:
    virtual void accept(Visitor* v) = 0;
};

class FloppyDisk : public Equipment
{
public:
    virtual void accept(Visitor* v);
};
void FlopyyDisk::accept(Visitor* v)
{
    v->visit(this);
}

class Chassis : public Equipment
{
public:
    virtual void accept(Visitor* v);
private:
    std::vector<Equipment*> m_parts;
};
void Chassis::accept(Visitor* v)
{
    for(int i = 0; i < m_parts.size(); ++i)
        m_parts[i]->accept(v);
    v->visit(this);
}

class Visitor
{
public:
    virtual void visit(FloppyDisk* floppyDisk) = 0;
    virtual void visit(Chassis* chassis) = 0;
};