Object Oriented Programming with D Language. Private access specifier. Summary.

[Chris R. Miller]

Jesse Phillips wrote:
> On Thu, 21 Aug 2008 07:11:15 -0400, DF wrote:
> 
>> Neil Vice Wrote:
>>
>>> DF wrote:
>>>> Robert Fraser Wrote:
>>>>
>>>>> DF wrote:
>>>>>> Why can private fields be accessed from other methods or classes in
>>>>>> the same module?
>>>>>>
>>>>>> If I wanted to access them from the same module I would make them
>>>>>> package public.
>>>>> It's a feature -- a replacement for "friend" in C++. The general
>>>>> idea of a module is that it is an autonomous code unit controlled by
>>>>> a single developer/team and if you're accessing a private function
>>>>> in the module, you have a good reason to. It's all the same file, so
>>>>> if you're changing something that accesses a private member, you can
>>>>> change the private implementation as well.
>>>>>
>>>>> "package" isn't implemented (sadly -- I find it very useful in Java
>>>>> so that a package has only a single public API).
>>>> Ok, thanks for your reply. But I think you've missed one thing. Let's
>>>> now speak of OO systems, about one basic principle of such systems
>>>> which is data abstraction. According to it an object should not
>>>> expose any of its implementation details. This means that you should
>>>> completely hide the way in which an object implements a message
>>>> handler from the rest of the program.That's one reason why all of
>>>> your instance variables (a class's nonconstant fields) should be
>>>> private. So what do you think on that D implementation of "private"
>>>> access specifier breaks data abstraction?
>>> If you implement a single class per module it isn't broken.
>>>
>>> By implementing multiple classes in a single module, as previously
>>> mentioned you are indicating that you consider the classes part of a
>>> single set of "implementation details" which are then hidden from other
>>> modules, again not broken.
>>>
>>> In this way it allows you to declare the level at which information
>>> hiding should be enforced.
>> I try to summary what I wanted to ask and say.
>>
>> 1) Why D language OO "private" access specifier is made "module public"
>> (e.g. method can be accessed by any other class or function inside the
>> same module, "private" field can be accessed and CHANGED by any other
>> class or function inside the same module)?
>>
>> -- To my point of view if you want to implement such a communication is
>> a single module between two classes or a function and a class just make
>> "module public" access specifier, "private" should be private (e.g.
>> restricts the access to the class itself. Only methods that are part of
>> the same class can access private members.)
>>
>> 2) What's the difference between module and package?
>>
>> -- Maybe that's where I'm wrong, because it is the same things to me.
> 
> A module is a single file, a package is all the files in that directory.
> 
> You are claiming that breaking the strict model laid out by Java, breaks 
> OOP.

Technically speaking OOP is a paradigm and no jargon is really concrete.
 It's fun to experiment with different implementations and see how they
work out.

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