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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: usefulness of "data hiding"
Newsgroups: comp.lang.ada
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Date: Sun, 18 Jan 2009 15:17:04 +0100
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Date: 2009-01-18T15:17:06+01:00
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On Sun, 18 Jan 2009 05:07:40 -0800 (PST), Graham Stark wrote:

> On Jan 16, 8:57�am, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
> wrote:
>> On Thu, 15 Jan 2009 16:51:38 -0800 (PST), Russ P. wrote:
>>> As many of you probably know, Python had no data hiding.
>>
>> Python is a dynamically typed language. When dynamic typing is considered
>> conceptually that inevitably leads you to weak and then to no typing. In an
>> effectively untyped framework (this includes massive type inference as
>> well), you necessarily have to drop encapsulation. There is nothing to
>> hide, and nothing can be hidden.
> 
> There's not much relationship between weak typing and data hiding, is
> there?
> 
> The least strongly typed language I know of is PHP
> ($s = "x" + 10; is legal, for instance)
> but you can have complete encapsulation if you want it:
> 
> class A{
>     private $a;
>     function getA(){ return $this->a; }
>     function setA( $a ){ $this->a = $a; }
> }
> 
> and there are strongly typed languages, like Pascal, where you can't
> do this at all.

In order to reason about these examples, you should tell me what was
dynamic and encapsulated in the examples you provided. I don't know PHP,
but "x" and 10 look like literals. That does not sound like dynamic typing. 

Again, I don't know PHP, but considering Ada's:

   type A is private;
private
   type A is new Integer;

Here the operation "+" of A is hidden. In a dynamically typed language you
cannot do it, the interface of any type has all possible operations. you
possibly can override implementations, but you cannot remove them. I don't
know what PHP would bind public "+" to in a comparable case. Would it be to
"method-not-understood" or to the original "+". Any choice breaks
encapsulation to me.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de