Operator of the day!

operator_of_the_day.cpp

#include <stdio.h>

void takes_int_reference(int &i) { i = 42; }

// Trivial wrapper example, a more appropriate use would be to wrap a resource
// which requires R.A.I.I. for safe usage.
class int_wrapper {
private:
    int i;
public:
    int_wrapper(int i) : i(i) {}
    void print() { printf("%d\n", i); }

    // Operator of the day! Allows passing the wrapper into functions as if it
    // was the type it is wrapping.
    operator int &() { return i; }
};

// This can also extend to generic wrappers
template<typename T>
class wrapper
{
    T val;
public:
    wrapper(T val) : val(val) {}

    // Note: This is not a reference meaning val will be copied leaving it 
    // unchanged.
    operator T() { return val; }
};

int main() {
    int_wrapper i(0);
    i.print();

    // Here we can pass the wrapper to a function which only...
    takes_int_reference(i);
    i.print();
}