/* * 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> /* * 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. */ int main() { int type; std::cout << "Demonstration of runtime binding.\n"; std::cout << "Type 1 for a vector of complexes;\n"; std::cout << "Type 2 for a vector of doubles: "; std::cin >> type; Printable* avec; switch (type) { case 1 : std::cout << "Constructing a CVector\n"; avec = new CVector(10, DComplex(0.0), DComplex(1.0) ); break; default : std::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() { std::cout <<"Vector of complex:\n"; // Inherit the operator<<() function of RWMathVec<DComplex>: std::cout << *this << "\n"; } void DVector::print() { std::cout <<"Vector of doubles:\n"; // Inherit the operator<<() function of RWMathVec<double>: std::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) ]