Object Oriented Programming with D Language. Private access specifier.

[DF]

Lars Ivar Igesund Wrote:

> DF wrote:
> 
> > Lars Ivar Igesund Wrote:
> > 
> >> DF wrote:
> >> 
> >> > Fawzi Mohamed Wrote:
> >> > 
> >> >> On 2008-08-21 09:59:35 +0200, DF <deefriend at ymail.com> said:
> >> >> 
> >> >> > 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?
> >> >> 
> >> >> There can be good reasons to break encapsulation (see C++ friend
> >> >> method). A language should make it easy to respect successful
> >> >> practices, support them, but not needlessly limit the programmer.
> >> >> A programmer should be a grown up person, as long as it is clear what
> >> >> is ok and what not, and doing the right thing is easy, all should be
> >> >> well.
> >> >> In Python for example all variables are actually private just by
> >> >> convention...
> >> >> 
> >> >> I find D approach very reasonable, it forces all the things that know
> >> >> the private interface to be in one place, namely one file.
> >> >> Suppose that you need to write a template specialization that needs
> >> >> access to private details... D approach is well suited.
> >> >> 
> >> >> Fawzi
> >> >> 
> >> > 
> >> > Nice reply. "A programmer should be a grown up person..." who told you
> >> > that? :) Just a joke.
> >> > 
> >> > "There can be good reasons to break encapsulation (see C++ friend
> >> > method)." - it is sad that you think so.You mixed up a good design
> >> > solution and a solution. (Here I want to say that PROBABLY you've
> >> > designed your OO system in a wrong way if you need to break an
> >> > encapsulation).
> >> > 
> >> > And I don't believe that one can't write "a template specialization
> >> > that
> >> > needs access to private details" in Java. (Where "private"  - restricts
> >> > the access to the class itself. Only methods that are part of the same
> >> > class can access private members.)
> >> 
> >> OO isn't the answer to everything - and Java's definition of OO is only
> >> one interpretation, and not necessarily the best. Java's strictness can
> >> in fact force you to unnecessarily complex design aka bad design.
> >> 
> >> --
> >> Lars Ivar Igesund
> >> blog at http://larsivi.net
> >> DSource, #d.tango & #D: larsivi
> >> Dancing the Tango
> > 
> > "OO isn't the answer to everything" - nobody said that. Just we speak
> > about writing OO systems in D language not about that OO is the answer to
> > everything. What considers Java I didn't write that Java is the best
> > "definition of OO".
> > 
> > Java's strictness can in fact
> > force you to unnecessarily complex design aka bad design - please give me
> > an example.
> 
> I see no need to do that, you are the one claiming that D is at fault which
> is at the core of this thread.
> 
> -- 
> Lars Ivar Igesund
> blog at http://larsivi.net
> DSource, #d.tango & #D: larsivi
> Dancing the Tango

It is easy to say that it's ok, than find out why it is ok.
I'm not saying that D implementation of "private" access specifier is wrong, I just want to know why "private" is implemented in this way.
Is it just because it solves language-specific problems or there is any other reason for that?