Adding a new design constraint to D

[Ola Fosheim Grøstad]

On Tuesday, 14 June 2022 at 20:04:14 UTC, Dom Disc wrote:
> On Tuesday, 14 June 2022 at 17:24:31 UTC, Ola Fosheim Grøstad 
> wrote:
>> On Tuesday, 14 June 2022 at 17:16:04 UTC, Dom Disc wrote:
>>> If it's a member, you can do nothing about it - not with 
>>> module level nor with class level privacy. Also not in C++ or 
>>> Java or any other language I know about.
>>
>> Not sure what you meant by this. You can make the member a 
>> class that has its own privacy with a selective set of friends.
>
> What I mean is: You cannot prevent a member function from 
> having access to the private variables of the class. Even if it 
> should not touch them.

This seems to compile:

```C++
class A {
public:
     inline void f();
     inline void g();
private:
     class X {
       int value;
       friend void A::f();
     };

     X x{};
};


void A::f(){
     x.value++;
}

void A::g(){
     //illegal: x.value++;
}
```