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This reminds me of the discussion about the FOR loop. In Oberon, Wirth eliminated it, because what it did could also be accomplished via WHILE, for instance. But in Oberon-2 he reintroduced it, not because it was so commonly used, IIRC, but because it was more elegant.
Rene
=============René A. Krywult
-------------------------------------------------
"Gûrberen," pent i naneth dî,
"mabapadan a ce darach sí!"
___________________________________
----- Original von: "Campbell, Robert D (UK Edinburgh)" <robert.d.campbell{([at]})nowhere.xy
>
>> I guess we agree that - on the pure Component Pascal level
>> - EXTENSIBLE RECORDs are unneccesary. The question was whether
>> EXTENSIBLE procedures are neccessary.
...
>> So with this the argument for EXTENSIBLE procedures vanished and they are
>> a matter of personal style as were EXTENSIBLE RECORDs and Fjodor is right,
>> both might - on the level of Component Pascal at least - be banned.
I think there is a flaw in the above conclusions, resulting from an unstated assumption.
People consider only what is NEEDED for correct function (usually using 'Initialisation'
as an example. There is also the question of what is DESIRABLE for correct function.
I give an example (taken from LibRandom, but there are many others).
This implements an ABSTRACT type meant to represent a mathematical object called
a Random Variate (or RV). These come in various flavours
with names such as 'Normal', 'Exponential', and in millions of
user specific flavours.
They can be (mathematically) described in many different
(but essentially equivalent) ways. Two of the most common
(and useful) are called the 'Pdf' and the 'Cdf'.
The ABSTRACT base type 'Variate' uses the (ABSTRACT) 'Pdf' to compute the 'Cdf'.
When Variate is extended to, for example, Exponential, it is NECESSARY to
implement the ABSTRACT base procedure Pdf, it is NOT NECESSARY to
implement the EXTENSIBLE procedure Cdf.
However, for the Exponential RV, Cdf has a very simple mathematical form and
it is very easy and very desirable (vastly faster, more accurate, simpler)
to reimplement Cdf as well.
On the other hand, for user defined RV's, it may be very difficult, if not impossible,
to reimplement Cdf directly, and depending on the application there may be no desire to
use the Cdf much anyway, so run-time efficiency is secondary to minimising coding effort.
The Component Pascal attribute EXTENSIBLE simply supports this 'optional'
reimplementation; I don't see an equally simple alternative.
Note that the above discussion has not used 'super' calls. Please ban these if you wish.
I, too, prefer 'upcalls' as suggested by Marc to 'super' calls.
Robert
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Received on Mon Oct 11 2004 - 15:27:59 UTC