How to properly return reference to class member?

[agnus]

Hi, suppose this class:

class Foo {
 
    protected:
    QPoint& bar() const;
 
    private:
    QPoint m_bar;
};
 
QPoint& Foo::bar() const {
    return m_bar;
}

class Foo {

    protected:
    QPoint& bar() const;

    private:
    QPoint m_bar;
};

QPoint& Foo::bar() const {
    return m_bar;
}

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I get this error:

error: invalid initialization of reference of type ‘QPoint&’ from expression of type ‘const QPoint’

However it works if I change it to this:

QPoint& Foo::bar() const {
    return (QPoint&) m_bar;
}

QPoint& Foo::bar() const {
    return (QPoint&) m_bar;
}

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1) I don't understand why the compiles says my QPoint is const.
2) Is it ok to leave the cast there?