基类静态引用数据成员上C ++对象切片行为的奇怪案例

我正在经历一个奇怪的对象切片案例。我在需要单例类的项目上工作，所以我的Base和派生类都是单例。以下示例案例描述了我的情况。

这是我的基础课

// Base.h
class Base
{
    public:

        static Base& base;

        virtual void doSomething(){ cout<<"Base Do Something"<<endl; }

    protected:

        Base();
        virtual ~Base();
        static Base& getBaseInstance();

    private:
};

//Base.cpp
Base::Base()
{
    //ctor
}

Base::~Base()
{
    //dtor
}

Base& Base::getBaseInstance()
{
    static Base object;
    return object;
}
Base& Base::base=Base::getBaseInstance();

这是我的派生类

class Derived: public Base
{
    public:

    static Derived& derived;
    virtual void doSomething(){ cout<<"Derive Do Something"<<endl; }

  static Derived& getDerivedInstance();
    protected:
        Derived();
        virtual ~Derived();

    private:
};

Derived::Derived()
{
    //ctor
}

Derived::~Derived()
{
    //dtor
}

Derived& Derived::derived=Derived::getDerivedInstance();

Derived& Derived::getDerivedInstance()
{
    static Derived object;
    return object;
}

最后这是我的主要功能

int main()
{
    cout << "Hello world!" << endl;
    Base::base.doSomething();
    Derived::derived.doSomething();

    Base::base=Derived::derived;

    Base::base.doSomething();

    Base::base=Derived::getDerivedInstance();

    Base::base.doSomething();

    Base& r = Derived::derived;

    r.doSomething();

    Base::base=Derived::getDerivedInstance();
    Base::base.doSomething();
    return 0;
}

我正在获得以下输出

Hello world!
Base Do Something
Derive Do Something
Base Do Something
Base Do Something
Derive Do Something
Base Do Something

所以我的问题是，对象切片不应在引用上起作用，那么为什么我不能Base::base用派生对象覆盖作为基类的静态数据成员创建的引用？虽然这可以正常工作Base& r = Derived::derived;

我的意思是，当我打电话给我做某事时，r.doSomething()我得到了派生类的doSomething。但是事实并非如此

    Base::base=Derived::derived;    
    Base::base.doSomething();

或者

    Base::base=Derived::getDerivedInstance();    
    Base::base.doSomething();

任何澄清将不胜感激。谢谢你。