Extending D's support for object-oriented design with private(this)

[Dom DiSc]

On Tuesday, 30 April 2024 at 00:01:00 UTC, NotYouAgain wrote:
> The source of all this, can be trace back to the D designer who 
> decided to change the "right and obvious" meaning of private.
>
> That was a mistake. It's not that the module private is wrong, 
> that certainly has a place, but changing the meaning of 
> private, was a mistake that D has to live with.

It's not "wrong". It's just a different philosophy, like with 
transitive const.
You can claim something is "logical const" but still modify 
internal state, or you enforce that something that is claimed 
const can really not be modified whatsoever.
Neither of the two is "wrong", it's just different and you can 
not easily translate between the two.
With private you can claim something is not accessed by other 
stuff within the same file (by declaring it "private to the 
class"), but this is only "logical private", because effectively 
if you have access to a file, you can access everything in that 
file, no matter how "private" it is.
But if something is in a different file, you can enforce that 
someone cannot access (aka modify) what is in there. Maybe simply 
by making the file readonly, but there are also stronger 
protection measures possible.

As I said in the other thread: A black-box test (for example 
something that tests the encapsulation of an object) shall not 
have the possibility to modify the object under test. So it 
cannot be in the same file. If you implement it in the same file 
and claim privacy, you are lying to yourself. It is simply not 
true.

In both cases (const and private) C++ allows the programmer to 
lie to himself (which is convenient, I confess) and D enforce 
correct behaviour (which is inconvenient at times).
I prefer the D philosophy.

I have nothing against private(this), it's convenient, you are 
right.
But I hate it if someone insist to call the other philosophy 
"wrong". That is what provoces so much resistence in these 
threads. Your chances to get the feature you want so much will 
become much higher, if you refreign from insulting others.