9.9 Example with Multiple Inheritance and Runtime Binding

FILENAME: example8.cpp

Program:

/*

 * Example illustrating the use of multiple inheritance
 * to do runtime binding. Although the Math.h++ class
 * library does not use any virtual functions, it is easy
 * enough to implement them in a derived class by using
 * multiple inheritance.
 */

#include <rw/math/mathvec.h>
#include <iostream.h>

/*
 * This is the abstract base class where the virtual 
 * functions that we plan to use are declared (but
 * not defined).
 */

class Printable 
{
public:
  virtual void           print() = 0;
};

/*
 * Here are two classes that inherit not only the 
 * abstract base class above, but also the properties of
 * a Math.h++ class. The first class will inherit
 * RWMathVec<DComplex>, the second RWMathVec<double>.
 */

class CVector : public RWMathVec<DComplex>,public Printable 
{
public:
  CVector(unsigned n, DComplex start, DComplex inc) : 
      RWMathVec<double>(n, start, inc) {}
  virtual void          print();

};

class DVector : public RWMathVec<double>, public Printable 
{
public:
  DVector(unsigned n, double start, double inc) : 
      RWMathVec<double>(n, start, inc) {}
  virtual void          print();
};

/*
 *  A little test program to illustrate.
 */

main()
{
  int type;

  cout << "Demonstration of runtime binding.\n";
  cout << "Type 1 for a vector of complexes;\n";
  cout << "Type 2 for a vector of doubles: ";
  cin >> type;

  Printable* avec;

  switch (type) 
{

  case 1 :
    cout << "Constructing a CVector\n";
    avec = new CVector(10, DComplex(0.0), DComplex(1.0) );
    break;
  default :
    cout << "Constructing a DVector\n";
    avec = new DVector(10, 0, 1);
  }

  /*
   * Note that "avec" points to the *base* class Printable.
   * The actual type of what it points to is unknown at
   * compile time --- it depends on what the user typed
   * above. Runtime binding happens for the virtual
   * function print().
   */

  avec->print();
}

void
CVector::print()
{
   cout <<"Vector of complex:\n";
   // Inherit the operator<<() function of RWMathVec<DComplex>:
   cout << *this << "\n";
}

void
DVector::print()
{
   cout <<"Vector of doubles:\n";
   // Inherit the operator<<() function of RWMathVec<double>:
   cout << *this << "\n";
}

Sample Input:

User input required.

Sample Output (shown for an input of "1"):

Demonstration of runtime binding.
Type 1 for a vector of complexes;
Type 2 for a vector of doubles: 1
Constructing a CVector
Vector of complex:
[
(0, 0) ( 1, 0) ( 2, 0) ( 3, 0) ( 4, 0)
(5, 0) ( 6, 0) ( 7, 0) ( 8, 0) ( 9, 0)
]