Re: Why use *protected* virtual functions for Template Method
Barry wrote:
private member function in the base class is not visible in the derived
class, only visible function can be overridden
Definitely no! You can not access the baseclass' private function, but you
can still override it, provided it is virtual. Also, visibility is not
affected by private/protected/public, only accessibility is.
code example, the virtual functions are overridden by private
functions in a derived class.
(Please I don't want this thread to stray into "should virtual
functions be non-public": this has been already covered in past
threads)
See this case:
class Ostream {
public:
Ostream& operator<< (int i) {
write(&i, sizeof(int));
return *this;
}
Ostream& operator<< (char c) {
write(&c, sizeof(char));
return *this;
}
protected:
virtual size_t write(void const* buf, size_t size) = 0;
};
class FileOstream : public Ostream {
private: // protected if you don't wanna seal FileOstream
virtual size_t write(void const* buf, size_t) {
// your implementation here
}
};
There is no reason not to make write() private. Further, you don't "seal"
the class if you make it private, a class derived from FileOstream can
override the function again.
Uli
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