#include <iostream>
using namespace std;
class foo {
public:
	int A() const {   // const function
    	return m_var; 
	}
	int const B() {   // non const function, but const return type
    	return m_var; 
	}
	int const& C() const {   // non const function, but const reference return type
    	return m_var; 
	}
private:
	int m_var; 
};
 
int main() {
	const foo x{}; 
	x.A();                // ok 
	//x.B();              // not ok -> function B() doesn't guarantee to leave x unchanged. 
	x.C();                // ok 
    const int& y = x.C(); // ok  (y will not alter m_var. 
    int& z = x.C();       // not ok since z is not const 
	return 0;
}

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