#include <iostream>

class ClassA
{
public:
	int a;
	ClassA():a(){}
	ClassA& Dup1(){
		return *this;
	}
	ClassA Dup2(){
		return *this;
	}
};

int main()
{
	ClassA a;

	const ClassA &dup1 = a.Dup1();
	const ClassA &dup2 = a.Dup2();

	a.a = 1;

	std::cout << "a.a  -> " << a.a << std::endl;
	std::cout << "dup1.a  -> " << dup1.a << std::endl;
	std::cout << "dup2.a  -> " << dup2.a << std::endl;
}

a.a  -> 1
dup1.a  -> 1
dup2.a  -> 0