Object Oriented Programming with D Language. Private access specifier.

[Lars Ivar Igesund]

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