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.

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).

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?

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.

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).

package is implemented to mean that something is accessible to other modules in the same package.


-- 
Lars Ivar Igesund
blog at http://larsivi.net
DSource, #d.tango & #D: larsivi
Dancing the Tango

On 2008-08-21 09:59:35 +0200, DF <deefriend@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

Fawzi Mohamed Wrote:

> On 2008-08-21 09:59:35 +0200, DF <deefriend@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.)

-- Thanks for your reply. Maybe I am wrong.

DF wrote:

> Fawzi Mohamed Wrote:
> 
>> On 2008-08-21 09:59:35 +0200, DF <deefriend@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

Lars Ivar Igesund Wrote:

> DF wrote:
> 
> > Fawzi Mohamed Wrote:
> > 
> >> On 2008-08-21 09:59:35 +0200, DF <deefriend@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.

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.