Why do private member variables behaved like protected in the same module when creating deriving class?

[David Gileadi]

On 10/26/18 12:27 PM, 12345swordy wrote:
> On Friday, 26 October 2018 at 18:45:32 UTC, Stanislav Blinov wrote:
>> On Friday, 26 October 2018 at 18:16:38 UTC, 12345swordy wrote:
>>> Mike Parker told me that this is intentional and not a bug.
>>
>> It's not a bug.
> Is this really necessarily?
> 
>> Why "however"?
> 
> Class private member variables are behaving like they protected class 
> protected when creating derived class in the same module.

[snip]

Whether this loophole is desirable and useful is a matter of opinion. It 
certainly is deliberate, though. I believe it may have been inspired by 
C++'s "friend" declarations. The comparison may help with understanding 
why D does it this way: https://dlang.org/articles/cpptod.html#friends

In my opinion it reflects D's ethos of keeping the common practice safe 
but attempting to always allow an escape hatch.