Manipulate class private member with externals functions and operators overload

[xgiovio]

//
//  main.cpp
//  Test
//
//  Created by Giovanni Di Grezia on 22/07/13.
//  Copyright (c) 2013 Giovanni Di Grezia. All rights reserved.
//
//
//
//


// pass an external function to a class acting on a private member

#include <iostream>
#include <string>
#include <exception>
#include <cmath>
#include <iomanip>

using namespace std;


/////////////// external function
int magia_su_numero (int input){
    return input *2;

}


///////////////////// test class
class test{
public:
    
    test(int input = 1)
    :numero(input)
    {}
    
    
    template <typename A> A do_funct (A passed_function(A) ){
        return passed_function(numero);
    }
    
    
    
private:
    int numero;
    
};

/////////////// overloaded operator >>

int operator>> (int funct_to_pass (int ), test & target){
    return ( target.do_funct(funct_to_pass)  );

}


    int main () {
        
        test obj;
        
        cout << (magia_su_numero >> obj) << endl;
        
        return 0 ;
    }