OOP_(re)

Wed, 4 Jun 1997 22:50:12 +0200 (MET DST)

According to Frank Heckenbach:
> 
> Look at it this way: If there's a field in the base class that not everybody
> needs, there's no way for those who don't need it to remove it by deriving
> a new class, so they'll have to carry something useless in their programs.

True.

> If, however, a field that some people need is not in the base class, they can
> just derive their own base class and forget about the old base class.

Sorry, but this is *not* true.  I had *lots* of problems with Turbo Vision
for this reason.

While generalizing Turbo Vision for graphics mode (thus creating BO3), it
was necessary to introduce new fields to `tView'.  Since I didn't have the
TV source (I didn't want to spend 600DM (~$400) for it (but finally did,
you know ...): ), I had to derive successor objects from *each* for-real-use
object: `tWindow', `tDialog', `tInputLine', ... it was not only bulk of work,
but also very unclean Pascal.  Once I had the TV source, I threw away BO3,
added the necessary fields to `tView' and essentially re-wrote TV (BO4.  My
next project of this kind, BO5, will be completely independend of TV (... like
BO2 was.  I had better continued BO2 rather than trying to use TV ...)).

This example (where to have fields) proves how difficult it is to design a
class library for general use.  It might be a good idea to introduce some
initially unemployed data fields in some base objects just for future use.
(Not in *the* base object, but somewhere higher in the hierarchy, where
space doesn't matter so much.)

> [Some small procedure ...]
> 
> (Better declare it as inline, though...)

\begin{off-topic}
  Or compile it with `-O3', so GPC will automatically inline it.
\end{off-topic}

Greetings,

    Peter

 Dr. rer. nat. [970604] Peter Gerwinski, Essen, free physicist and programmer
peter.gerwinski@uni-essen.de - http://home.pages.de/~peter.gerwinski/ [970201]
 maintainer GNU Pascal [970510] - http://home.pages.de/~gnu-pascal/ [970125]

Peter Gerwinski (peter@agnes.dida.physik.uni-essen.de)