一些疑问

看到书上的代码之后，产生了一些疑问，还请大佬指教一下
程序如下：

#include<iostream>
using namespace std;
class Base1{
    public:
        virtual void display()const;
};
void Base1::display()const{
    cout<<"Base1::display()"<<endl;
}
class Base2:public Base1{
    public:
        void display()const;
};
void Base2::display()const{
    cout<<"Base2::display()"<<endl;
}
class Derived:public Base2{
    public:
        void display()const;
};
void Derived::display()const{
    cout<<"Derived::display()"<<endl;
}
void fun(Base1 *ptr){
    ptr->display();
}
int main()
{
    Base1 base1;
    Base2 base2;
    Derived derived;
    fun(&base1);
    fun(&base2);
    fun(&derived);
    return 0;
}

这是书上讲虚函数的时候的那道例题
………………………………………………………………………………………………………………………………………………………………………………………………………………
第一个疑问：
我把虚函数去掉，想试用一下赋值兼容规则，程序变成了下面的样子

#include<iostream>
using namespace std;
class Base1{
    public:
         void display()const;
};
void Base1::display()const{
    cout<<"Base1::display()"<<endl;
}
class Base2:public Base1{
    public:
        void display()const;
};
void Base2::display()const{
    cout<<"Base2::display()"<<endl;
}
class Derived:public Base2{
    public:
        void display()const;
};
void Derived::display()const{
    cout<<"Derived::display()"<<endl;
}
void fun(Base1 *ptr){
    ptr->display();
}
int main()
{
    Base1 base1;
    Base2 base2;
    Derived derived;
    fun(&base1);
    fun(&base2);
    fun(&derived);
    return 0;
}

但是呐，运行结果不尽人意

因为呐，书上将赋值兼容规则的时候是把display（）声明为内联函数的，这里我就不是很明白为什么会这样了……还请大佬指导一下
……………………………………………………………………………………………………………………………………………………………………………………………………
第二个问题
我把第12行和14行的const去掉了

#include<iostream>
using namespace std;
class Base1{
    public:
        virtual void display()const;
};
void Base1::display()const{
    cout<<"Base1::display()"<<endl;
}
class Base2:public Base1{
    public:
        virtual void display ();
};
void Base2::display(){
    cout<<"Base2::display()"<<endl;
}
class Derived:public Base2{
    public:
        void display()const ;
};
void Derived::display()const{
    cout<<"Derived::display()"<<endl;
}
void fun(Base1 *ptr){
    ptr->display();
}
int main()
{
    Base1 base1;
    Base2 base2;
    Derived derived;
    fun(&base1);
    fun(&base2);
    fun(&derived);
    return 0;
}

结果就变化了……这个也请大佬讲解一下