Remove friend class dependency in the following case

Question

class foo
{
    bar b;

    someFunction()
    {
        b.alphaObj->someFunctionOfAlpha();
    }
};


class bar
{
    friend class foo;
    // many more friends

private:
    alpha *alphaObj;
};

How do I remove the friend dependency without exposing the private members with getters and setters. I understand friend classes could help in enhancing encapsulation but there are a lot of friend classes defined in my class exposing the private members to all. Hence I am thinking of a better approach and any help is appreciated.

Requiring a lot of friends indicates a set of poorly encapsulated classes - Why do so many classes require access to class bar? — Tom
– Tom, Commented Dec 10, 2019 at 9:41
We are dealing with legacy code here and that's how it is. We are thinking of refactoring now with a better design — abhilash anand
– abhilash anand, Commented Dec 10, 2019 at 9:44
The example here feels a bit too generic to be useful. Generally someFunctionOfAlpha wants to be moved to some other class where it can be made public. It could potentially be a wrapper that say bar creates, or become a member of bar itself. Another option is to pass a callback function and call that, instead of calling whatever it is directly. — Fire Lancer
– Fire Lancer, Commented Dec 10, 2019 at 9:44

463035818_is_not_an_ai · Accepted Answer · 2019-12-10 10:51:53Z

1

Independent of your friend issue, being required to write this

b.alphaObj->someFunctionOfAlpha();

is not the best design. You should rather call (*):

b.someFunctionOfAlpha();

Now it is also obvious how to remove the friends:

class bar
{
public:
    void someFunctionOfAlpha() { alphaObj->someFunctionOfAlpha(); }

private:
    alpha *alphaObj;
};

(*) This guideline has a name, I just cannot find it at the moment. In general, calling a method should be like: "Do that!". Calling a method should not be like "Show me your internals so I can do what I want".

edited Dec 10, 2019 at 10:51

answered Dec 10, 2019 at 9:52

463035818_is_not_an_ai

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6 Comments

abhilash anand Over a year ago

Thank you. This answer shows a valid point but does not answer the question. Hence not marking as correct

463035818_is_not_an_ai Over a year ago

@abhilashanand why does it not answer the question? I show you how you can resolve the need for friend

abhilash anand Over a year ago

Yes. But this exposes the inner features of alpha class indirectly by making it public. I have mentioned it as a constraint to not expose the inner functionalities by means of getters and setters

abhilash anand Over a year ago

We had a discussion and this was pretty good and hence marked as correct. Another suggestion was the make the member public and make it a const such that it cannot be modified. If there are a lot of variables then your suggestion could result in a lot of code. Thanks for your effort

abhilash anand Over a year ago

I think you are referring to "Law of Demeter" above :)

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