treehouse/content/programming/languages/cxx/access-modifiers-as-labels.tree

%% title = "C++ syntactic pitfall: access modifiers as labels"

% id = "01H9R1KJES39Z6RBCKY4E71PYD"
- although Java and C#'s approach to symbol privacy may be verbose, it has one great advantage: it is stateless.

% id = "01H9R1KJES17626QXYEGM7XBC7"
- the way they're implemented in C++, it's essentially a bit more parsing state you have to keep track of

    % id = "01H9R1KJESG4K8T1K1G36T7HBP"
    - and you know what other parsing state you have to keep track of in C++? - that's right, the preprocessor.\
    access modifiers, like all tokens, are affected by the preprocessor, and you have to take that into account.

        % id = "01H9R1KJESJ0G0VQAW994ZHR0S"
        - take the following example:

        ```cpp
        class ComfyZone
        {
            std::vector<SoftBed> _soft_beds;

        #if ENABLE_HUGS

        public:
            void hug(Person& person);

        #endif

            int _remaining_hugs = 10;
        };
        ```

            % id = "01H9R1KJESDDX4089WVHVV8N3H"
            + although quite contrived, it illustrates the problem pretty well

                % id = "01H9R1KJESD2KED5TAFBY426A6"
                - (before you ask, `_remaining_hugs` needs to be always present because it has to be (de)serialized no matter if hugging functionality is compiled in. otherwise we'd get data loss.)

            % id = "01H9R1KJESES27VKVW4A0ZVM11"
            - we intended for `_remaining_hugs` to be private, but if hugs are enabled, it becomes public.

                % id = "01H9R1KJESTKW90R788SSPMNC6"
                - this can be _very_ hard to spot if you have a big class with lots of declarations inside.

        % id = "01H9R1KJESCJ3VC8ATPYFDCPSP"
        - this can be worked around by banning access modifiers from appearing in `#ifdef`s, but you have to _realize_ that this might happen

            % id = "01H9R1KJES4ZYHVADDF80WAXH6"
            - and I've seen instances of this exact thing occurring in the Unreal Engine codebase, which is _full_ of long lists of declarations (made even longer by the prevalence of `UPROPERTY()` specifiers)

% id = "01H9R1KJES182MCV2V0A4VHKKX"
- even if we didn't have the preprocessor, that access modifier is state _you_ have to keep track of

    % id = "01H9R1KJESH7PWNKCKW3H0WJHW"
    - I very often find myself needing to scroll upward after `<kbd>Ctrl</kbd>`{=html}-clicking on a field or function declaration, just to find out if I can use it

        % id = "01H9R1KJESFE6F1D4J5PA5Q381"
        - (thankfully IDEs are helpful here and Rider shows you a symbol's visibility in the tooltip on hover, but I don't have Rider on code reviews)