Using closure in function scope to make "real" private class members

[Dom Disc]

On Sunday, 5 June 2022 at 19:48:03 UTC, Ola Fosheim Grøstad wrote:
> On Sunday, 5 June 2022 at 19:41:36 UTC, Dom Disc wrote:
>> Anybody can declare friends, without even touching the file 
>> where the class is defined, and thereby access things that 
>> shouldn't even be visible to them (implementation details or 
>> even security relevant things)!
>
> No, I don't think so:
>
> «If a program contains more than one definition of a type, then 
> each definition must be equivalent.»

?!?
You don't need to re-declare the class. You can simply overwrite 
a friend function. Ok, if the class don't have any friends, this 
doesn't work. But most of the time there are some...