Inherit from const class

Question

I would like to inherit from a class with the const specifier like this:

class Property
{
    int get() const;
    void set(int a);
};

class Co         


        

Answer 1

I had the same need and I ended up with this quite manual approach :

class A
{
public:

    void fooMutable(void) {}
    void fooConst(void) const {}
};

class B : private A
{
public:

    using A::fooConst;
    const A& getParent(void) const
    {
        return *this;
    }
};

void fooParent(const A&) {}

int main(void)
{
    auto b = B{};
    b.fooConst(); // Ok
    b.fooMutable(); // Fail
    fooParent(b); // Fail
    fooParent(b.getParent()); // Ok

    return 0;
}

Note that the using keyword would not work with overloads const/mutable :

class A
{
public:

    void foo(void) {}
    void foo(void) const {}
};

class B : private A
{
public:

    using A::foo; // Expose the const and the mutable version
};

To solve this you could redefine the function yourself and call the parent :

class B : private A
{
public:

    void foo(void) const
    {
        A::foo();
    }
};

It can become pretty time consuming if you're inheriting a large hierarchy, but if it's for a not-so-big class it should be very reasonable and being quite natural for the user.