virtual template : virtual template « template « C++ Tutorial

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3. virtual template

/* The following code example is taken from the book
 * "C++ Templates - The Complete Guide"
 * by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002
 *
 * (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 */
#include <iostream>

class NotVirtual {
};

class Virtual {
  public:
    virtual void foo() {
    }
};

template <typename VBase>
class Base : private VBase {
  public:
    // the virtuality of foo() depends on its declaration
    // (if any) in the base class VBase
    void foo() {
       std::cout << "Base::foo()" << '\n';
    }
};

template <typename V>
class Derived : public Base<V> {
  public:
    void foo() {
       std::cout << "Derived::foo()" << '\n';
    }
};

int main()
{
    Base<NotVirtual>* p1 = new Derived<NotVirtual>;
    p1->foo();  // calls Base::foo()

    Base<Virtual>* p2 = new Derived<Virtual>;
    p2->foo();  // calls Derived::foo()
}

Base::foo()
Derived::foo()