I don't think that this is a good idea because friendship is granted by the
class itself and not the user of the class. That is, you're proposing that
a user should be able to access different fields which is nonsensical. It
is the class who decides which members are public or private etc and to
whome to grant friendship.



On Sun, 17 Jul 2022, 23:31 Frederick Virchanza Gotham via Std-Proposals, <
std-proposals_at_[hidden]> wrote:

> Recently I was working with an RS232 library when programming a
> microcontroller in C++. I needed a little finer control over the library's
> inner workings, more control than the library provided. I had to edit the
> library's header file to change the visibility of one of the class's member
> variables, I changed it from 'private' to 'public', and also I made one of
> the member functions 'public'. Alternatively I could have added one line at
> the end of the class definition:
>
> friend class MyOwnClass;
>
> and then I could have accessed all the private members through static
> member functions belonging to MyOwnClass.
>
> I propose that we should be able to "impose friendship" without editing
> the library's header files. For example:
>
> class Foo { int monkey; };
>
> int main(void)
> {
> Foo obj;
>
> using friend Foo;
>
> obj.monkey = 5;
> }
>
> The statement "using friend Foo" only has an effect within 'main', similar
> to how "using namespace std" would have limited scope here.
>
> Alternatively, the syntax could be on an access-by-access basis, something
> like as follows:
>
> int main(void)
> {
> Foo obj;
>
> friend<obj>.monkey = 5;
> }
>
> or the syntax could be:
>
> friend<obj.monkey> = 5;
>
> or maybe:
>
> std::friend(obj, monkey) = 5;
>
> or:
>
> friend >> obj.monkey = 5;
>
> Some of you might be thinking: "Why affirm such subterfuge when the author
> of the library obviously didn't want you messing around in there?", well
> computer programming isn't an exact science. Indeed we have paradigms and
> design patterns, but really at the end of the day we're trying to get
> things done, and this might mean following the instructions from Step 1 to
> Step 9 but then deviating at Step 10.
>
> Being able to manually impose friendship when and where you need it, would
> mean not needing to edit the 3rd party library's header file.
> --
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