Object Oriented Programming with D Language. Private access specifier.

[Lars Ivar Igesund]

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
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