C ++从const对象中返回非const引用

Question

I have structure that contains reference in it

template <class T>
struct RefContainer {

    RefContainer(T& t) : _r(t) {}

    T& getRef() {
        return _r;
    }

private:
    T& _r;
};

Now, another object, which is immutable uses this structure inside itself and has this object in it like so:

RefContainer<char> _c;

When I use that immutable object to transform itself with a dot I get a const reference. Since I call getRef of RefContainer object inside the immutable objects compiler says I violate const correctness.

The RefContainer itself has to hold non-const lvalue reference but I'd love to chain calls on immutable object to create new ones like so:

ImmubableObject obj;
auto newObj = obj.copyWithSomeAttributes().modifyWithThisString("str");
// I'm on C++11 btw, so I can use everything C++11 has to offer

How do I work this out the "right" way (possibly avoiding ugly const casts) ?

Answer 1

You should try something like this:

template <class T>
struct RefContainer {

    RefContainer(T& t) : _r(t) {}

    T& getRef() const {
             // ^^^^^
        return _r;
    }

private:
    T& _r;
};

This way, the T& reference can be used as non const, regardless the RefContainer instance is a const object or not.