/*
File: oop5.cpp

Returning a callable object is more awkward, 
since we must return an Int2Int reference or
an Int2Int pointer.
*/


#include <iostream>
using namespace std ;

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

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


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

class AddX : public Int2Int {

private:
   int m_offset ;

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

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


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

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


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


class IncX : public Int2Int {
public:
   int operator()(int n) { return n+1 ; }
} ;


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

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


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

Int2Int& select(int n) {
    static AddX add3(3) ;  // really should be const
    static AddX add5(5) ;
    static Mult3 times3 ;
    static IncX finc ;

    switch (n) {
       case 0 : return add3 ;
       case 1 : return add5 ;
       case 2 : return times3 ;
       default : return finc ;
    } ;
}

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

Int2Int* pick(int n) {
    static AddX add3(3) ;  // really should be const
    static AddX add5(5) ;
    static Mult3 times3 ;
    static IncX finc ;

    switch (n) {
       case 0 : return &add3 ;
       case 1 : return &add5 ;
       case 2 : return &times3 ;
       default : return &finc ;
    } ;
}


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


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 ;
   }

   Int2Int& plus3 = select(0) ;
   apply (plus3, B, 10) ;

   printf("\n\nAfter calling apply(plus3, B, 10):\n") ;
   for (int i=0 ; i < 10 ; i++) {
      cout << "   B[" << i << "] = " << B[i] << endl ;
   }

   Int2Int& plus5 = select(1) ;
   apply (plus5, B, 10) ;

   printf("\n\nAfter calling apply(plus5, B, 10):\n") ;
   for (int i=0 ; i < 10 ; i++) {
      cout << "   B[" << i << "] = " << B[i] << endl ;
   }

   apply (select(2), B, 10) ;

   printf("\n\nAfter calling apply(select(2), B, 10):\n") ;
   for (int i=0 ; i < 10 ; i++) {
      cout << "   B[" << i << "] = " << B[i] << endl ;
   }

   Int2Int *fptr ;

   fptr = pick(0) ;  // add3
   apply (*fptr, B, 10) ;
   printf("\n\nAfter calling apply(*fptr, B, 10):\n") ;
   for (int i=0 ; i < 10 ; i++) {
      cout << "   B[" << i << "] = " << B[i] << endl ;
   }


   fptr = pick(1) ; // add5
   apply (*fptr, B, 10) ;
   printf("\n\nAfter calling apply(*fptr, B, 10):\n") ;
   for (int i=0 ; i < 10 ; i++) {
      cout << "   B[" << i << "] = " << B[i] << endl ;
   }


}