Publicizing privately inherited members
When you inherit privately, all the
public members of the base class become private. If you want any
of them to be visible, just say their names (no arguments or return values)
along with the using keyword in the public section of the
derived class:
//: C14:PrivateInheritance.cpp
class Pet {
public:
char eat() const { return 'a'; }
int speak() const { return 2; }
float sleep() const { return 3.0; }
float sleep(int) const { return 4.0; }
};
class Goldfish : Pet { // Private inheritance
public:
using Pet::eat; // Name publicizes member
using Pet::sleep; // Both overloaded members exposed
};
int main() {
Goldfish bob;
bob.eat();
bob.sleep();
bob.sleep(1);
//! bob.speak();// Error: private member function
} ///:~
Thus, private inheritance is
useful if you want to hide part of the functionality of the base
class.
Notice that giving
exposing the name of an overloaded function exposes all the
versions of the overloaded function in the base class.
You should think carefully before using
private inheritance instead of composition; private inheritance
has particular complications when combined with runtime type identification
(this is the topic of a chapter in Volume 2 of this book, downloadable from
www.BruceEckel.com).
