Essential C++

5.3. Polymorphism without Inheritance

The num_sequence class of Section 4.10 simulates polymorphism. Each class object can be made into any of the six numerical sequences at any point in the program through the set_sequence() member function:

for ( int ix = 1; ix < num_sequence::num_of_sequences(); ++ix ) 
{ 
      ns.set_sequence( num_sequence::nstype( ix )); 
      int elem_val = ns.elem( pos ); 
      // ... 
} 

The ability to change the sequence type of ns is supported through programming rather than through direct support of the language. Each class object contains an _isa data member that identifies the current numeric sequence that it represents:

 class num_sequence { public: // ... private: vector<int> *_elem; // addresses current element vector PtrType _pmf; ...