----boundary-LibPST-iamunique-1853224215_-_-
Content-type: text/plain
----- Original von: Fyodor Tkachov <fyodor.tkachov{([at]})nowhere.xy
>> > Any (normal) procedure may be
>> activated by any"one", a method only by the owner, i. e. an object of
>>the correct type.
>
>There is no practical difference between o.Init and Module.Init( o ) >because in order to perform the latter call one still has to have an object >(o) of the correct type.
>The only difference is the explicit appearance of Module in the second >case, which I maintain only adds to clarity of the code.
May I disagree? Just imagine you have a binary tree with graphical objects, which are alle descendants of an object of Type "GraphicalObject.Object". Now, for any reason, you want to initialize a node. Using Module.Init(o), you have to know (that means checking!!) what object it is. By using its underlying Init, you need not know anything detailed about the object. Not only that you would have to CHECK every object, it would also be necessary to add all descendant modules to your code that handles general object operation. So, either you could not do those general operations where they belong (in Module GraphicalObject), or you whould have to include all descendant objects into the same basic module (which is quite bad to work with).
>> Of course you can avoid OOP alltogether and the code may even be
>>more effective.
>> But I believe encapsulation to be quite useful.
>
>All this has nothing to do with encapsulation.
I think it has, see the above.
>Coming back to your chain of three types A, B, C, inheriting from each >other, A and B being ABSTRACT, and C being LIMITED, all defined (as >you proposed) in separate modules (call them ModuleA, ModuleB and >ModuleC).
>Suppose instead of (extensible) methods like (a: A) Init() one has >procedures like ModuleA.Init( a: A ), etc.
>ModuleB.Init( b: B ) only has to make a proper call to ModuleA.Init -- >and C does not need to know how B is implemented -- how it calls >ModuleA.Init, etc.
>A perfect encapsulation, so far as I can see.
See above.
>If one inherites from the type B, one knows which module the type B is >defined in (ModuleB), and one automatically has access to procedures in >ModuleB.
Definitely wrong. The key to OOP is, that there are circumstances, where I do not know (and do not NEED to know) what kind of object there is EXACTLY, and where it is sufficient to know the base type.
>So writing b.Init instead of ModuleB.Init( b ) hides exactly nothing, and >only saves typing the module name.
Nah!
>Supercalls are completely superfluous and are replaced by calls to >ordinary procedures.
>To reiterate: a type one inherits from always belongs to some known >module, therefore one has access to the procedures in that module,
>including whatever initialization procedures one might need for hidden
>fields.
This assumption is plainly wrong.
N. Wirth, in a very recent publication, says: "Whereas in strongly types languages, such as Algol, Pascal, and Modula, every constant, variable, or function has a fixed type, recognizable from the program text, Oberon allows to define hierarchies of types, and to determine the actual type of a variable (within the hierarchy) at run-time. This, together with records containing fields of procedural types, is the stem of object-oriented programming. Such records are then called objects, and the procedural fields are called methods." (http://www.oberon.ethz.ch/wirthPiO/Preface.doc).
Now, I know that Wirth is not the Bible, nor is he Marx, but it is a fact that the key feature of OOP is *not* needing to know the exact type of an object at runtime. It is enough to know a BaseType and let the object itself handle how it actually behaves. If you don't need that feature, you don't need Oberon. Use Modula-2.
Rene
Rene
-------------------------------------------
Versendet durch AonWebmail (webmail.aon.at)
Powered by the E-mail PIM - Info Select - www.miclog.com
--------------------------------------------
To unsubscribe from this mailing list, send a message containing the word "unsubscribe" to:
blackbox-request{([at]})nowhere.xy
To get a list of valid e-mail commands and instructions on their usage, send a message containing the word "help" to the above address.
Send any problem reports or questions related to this email list to the list owner at
owner-blackbox{([at]})nowhere.xy
Current posting policy:
a) To post you should use the same address by which you are subscribed to the mailing list. That way, the list server will recognize you as subscriber and forward your posting immediately, without creating any overhead.
b) If, for some reason, you cannot post from the address, by which you are subscribed, your message will be moderated to avoid spam. Please understand that moderation will often cause some delay, in particular over weekends or holydays.
----boundary-LibPST-iamunique-1853224215_-_-
Content-type: application/rtf
Content-transfer-encoding: base64
Content-Disposition: attachment; filename="rtf-body.rtf"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=
----boundary-LibPST-iamunique-1853224215_-_---
Received on Mon Oct 04 2004 - 12:19:47 UTC