you lose the guarantee that when you look at a class's interface, you see
its entire interface. Adding friends from the outside (and, accordingly,
methods) is a very bad idea, because. encapsulation and invariants become
empty zilch

вс, 17 июл. 2022 г. в 23:24, Anoop Rana via Std-Proposals <
std-proposals_at_[hidden]>:

> 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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>>
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