/*
File: oop3.cpp

... a variation of the previous example ...
If the pure virtual () operator in the abstract base class is defined as
a const function, then the apply() function can be given a temporary
object produced by the constructor without storing it in a variable:

   apply (AddX(5), B, 10) ;

*/


#include <iostream>
using namespace std ;

//-------------------------------------------

class Int2Int {
public:
   virtual int operator() (int) const = 0 ;  // pure virtual
} ;


//-------------------------------------------

class AddX : public Int2Int {

private:
   int m_offset ;

public:
   AddX(int offset = 0) { m_offset = offset ; }

   int operator()(int m) const { return m + m_offset ; }
} ;


//-------------------------------------------

class Mult3 : public Int2Int {
public:
   int operator()(int m) const { return 3*m ; }
} ;


//-------------------------------------------

void apply(const Int2Int& f, int A[], int n) {
   for (int i=0 ; i < n ; i++) {
      A[i] = f( A[i] ) ;
   }
}


int main () {
   int B[10] = { 10, 11, 12, 13, 14, 15, 16, 17, 18, 19} ;


   printf("Before:\n") ;
   for (int i=0 ; i < 10 ; i++) {
      cout << "   B[" << i << "] = " << B[i] << endl ;
   }

   apply (AddX(3), B, 10) ;

   printf("\n\nAfter calling apply(AddX(3), B, 10):\n") ;
   for (int i=0 ; i < 10 ; i++) {
      cout << "   B[" << i << "] = " << B[i] << endl ;
   }

   apply (AddX(5), B, 10) ;

   printf("\n\nAfter calling apply(AddX(5), B, 10):\n") ;
   for (int i=0 ; i < 10 ; i++) {
      cout << "   B[" << i << "] = " << B[i] << endl ;
   }

   apply (Mult3(), B, 10) ;

   printf("\n\nAfter calling apply(Mult3(), B, 10):\n") ;
   for (int i=0 ; i < 10 ; i++) {
      cout << "   B[" << i << "] = " << B[i] << endl ;
   }
}