一些疑問

看到書上的代碼之后，產生了一些疑問，還請大佬指教一下
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;
}

這是書上講虛函數的時候的那道例題
………………………………………………………………………………………………………………………………………………………………………………………………………………
第一個疑問：
我把虛函數去掉，想試用一下賦值兼容規則，程序變成了下面的樣子

#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;
}

但是吶，運行結果不盡人意

因為吶，書上將賦值兼容規則的時候是把display（）聲明為內聯函數的，這里我就不是很明白為什么會這樣了……還請大佬指導一下
……………………………………………………………………………………………………………………………………………………………………………………………………
第二個問題
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;
}

結果就變化了……這個也請大佬講解一下