在public const修饰符中使用变量

Question

I'd like to have a variable in my class that is const when accessed from public scope and non- const when accessed from a private or protected scope. I'd like to avoid having a getter-method that returns a const reference to the variable. I tried messing around with the using keyword, but no success so far. Ideally it would look something like this:

class Foo
{
public:
    using var = const m_var; // This is of course gibberish
private:
    int m_var;
}

I could add a public const reference member variable and let it point to the private variable, but that way my class would get 4 bytes bigger, which I would like to avoid. Would a compiler realize that and optimize out that reference?

Any other ideas on how to solve the problem?

Answer 1

I'd like to avoid having a getter-method that returns a const reference to the variable

I don't know why you'd like to avoid that. This sounds like exactly what you want (perhaps just returning by-value):

class Foo
{
public:
    int getVar() const { return m_var; }
protected:
    int m_var;
};

If you have protected or private access to Foo , you can just m_var . If you don't, then you have a public const getVar() that doesn't let you modify it.

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There's really no other way of doing this. You can't overload on access rights in the way you can have overload on const -qualification or ref-qualification since overload resolution happens before access checking. That prohibits you from doing something like having a protected and public overload where the protected overload is the better match.

You also can't add aliases for variables without introducing actual references - but at that point you're making your class bigger but you still are using different names to reference the public and protected anyway, at which point using the public accessor member function is strictly better.