user defined conversion c++ using operator keyword - const or no const [duplicate]

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• What is the meaning of a const at end of a member function? 3 answers

With user defined conversion in C++ using the operator keyword, for example

class X {
private:
   int _x;
public:
   operator int() const { return _x; } 
};

how does the const qualifier change anything vs. not have a const qualifier? It seems that regardless of having const or no const, I would still need to assign to an lvalue like this:

X x;
const int &foo = x;