Re: [BLACKBOX] Upcalls deprecated

From: [at]} <CFB>
Date: Tue, 4 Mar 2008 12:42:55 +1030

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>-----Original Message-----
>From: BlackBox [mailto:BLACKBOX{([at]})nowhere.xy
>Aubrey.McIntosh{([at]})nowhere.xy
>Sent: Monday, 3 March 2008 10:30 PM
>To: BLACKBOX{([at]})nowhere.xy
>Subject: [BLACKBOX] Upcalls depreciated
>
>After almost 20 years, I seem to be learning a lot of Oberon
>thinking this week.
>
>I read in the Language Reference for Component Pascal that
>procedure calls and super calls are considered obsolete.
>
>What is the replacement? I was looking at HostPackedFiles and
>noticed that there are not any, there are type bound methods
>and the "Directory" construct. Is that the currently
>recommended practice?
>What is the motivation? Since it gets in the way of some
>clever thing I am considering, I assume it is a safety measure.
>
>

1. From the What's New in Component Pascal:

"Super calls

Because of the so-called semantic fragile base class problem, it is
recommended to avoid super calls whenever possible. It is possible to design
new software such that they are not needed, by relying on composition rather
than on implementation inheritance. Super calls are considered to be an
obsolete feature. For the time being, they are retained for backward
compatibility. In the long run, support for super calls may be reduced."

2. From "Component Software - Beyond Object-Oriented Programming" by Clemens
Szyperski (of Blackbox fame) and others:

"The essence of the semantic fragile base problem is how can a subclass
remain valid in the presence of different versions and evolution of the
implementation of its superclasses? ... To answer this question, the very
nature of implementation inheritance needs to be understood first."

This is followed by a page of explanation with the note: "For many, this is
probably difficult reading ..."

http://research.microsoft.com/~cszypers/Books/component-software.htm

3. I previously said as part of a discussion here with the subject 'RE: An
extended discussion of extensibility' (12 Oct 2004):

"By all means *discourage* the use of super calls but don't *ban* them
unless you want to restrict the use of Component Pascal to the BlackBox
framework and hinder more widespread adoption of the language.

Super calls are currently required if you are using Component Pascal with
Microsoft's .NET framework. Not only does this framework allow Component
Pascal to exploit features of future versions of Windows, it also currently
allows Component Pascal to be used to develop Linux applications via the
Mono project.

Also, banning super calls may limit the usefulness of Component Pascal as a
language with any other future OO-based framework whose
implementation you have no control over."

Regards,
Chris

Chris Burrows
CFB Software
http://www.cfbsoftware.com/

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Received on Tue Mar 04 2008 - 03:12:55 UTC