把ctor和非成员函数虚化

#include <iostream>//virtual ctor// firstclass NLcomponent{public:    virtual NLcomponent* clone() = 0;    //...};class TextBlock : public NLcomponent{public:    virtual TextBlock* clone() { }};class Graphic : public NLcomponent{public:    virtual Graphic* clone() { }};class NewLetter{public:    //...private:    list<NLcomponent*>components;};//////////////////////////////////////////////////////////////////////secondclass NewLetter{public:    NewLetter(istream& str);private:    list<NLcomponent*>components;};NewLetter::NewLetter(istream& str){    while(str)    components.push_back(readComponent(i_str));    //readComponent is a like ctor,请注意，NLcomponent是一个抽象基类    //构造函数的虚化我认为就是这里，    //...}//////////////////////////////////////////////////////////////////////third   ***copy ctor***class NLcomponent{public:    virtual NLcomponent* clone() = 0;    //...};class TextBlock : public NLcomponent{public:    virtual TextBlock* clone()     {return new TextBlock(*this) }};class Graphic : public NLcomponent{public:    virtual Graphic* clone()     {return new Graphic(*this) }};class NewLetter{public:    NewLetter(NewLetter&);    //...private:    list<NLcomponent*>components;};NewLetter::NewLetter(NewLetter& rhs){    //迭代遍历rhs的list，运用每一个元素的virtual copy ctor    //讲元素复制到此对象的component list 中，一下代码的细节讨论    //    for(list<NewLetter>::const_iterator it = rhs.components.begin()        ; it != rhs.end() ; it ++ )    {        components.push.back((*it)->clone);        //it只想当前元素，所以调用元素的clone函数取得元素的一个副本        //然后将副本加到component list尾端    }}//virtual non_fcn// 简易版class NLcomponent{public:    virtual ostream& operator<< (ostream&) = 0;    //...};class TextBlock : public NLcomponent{public:    virtual ostream& operator<< (ostream&) { }};class Graphic : public NLcomponent{public:    virtual ostream& operator<< (ostream&) { }};// 并没有考虑class NewLetterTextBlock T;T<< cout;// T.operator<<(cout);/*    virtual ostream& operator<< (ostream& os)     {        //假设int i ==> mem_data        os << i ;        return *this;    }*///完整版class NLcomponent{public:    virtual ostream& print (ostream&) = 0;    //...};class TextBlock : public NLcomponent{public:    virtual ostream& print (ostream&) { }};class Graphic : public NLcomponent{public:    virtual ostream& print (ostream&) { }};inline ostream& operator<<(ostream & os, NewLetter& c){    c.print(os);}/*首先，他可以inline，一般的虚函数是不能inline，然后这是一个妄图把非虚函数虚化    上面其实有觉得，虚化这一过程，总是在他的派生类分出明细，在另一个非继承体系    类来统一调用/实施，*/