Re: Persistence and supercalls under BlackBox

From: [at]} <Venkat>
Date: Mon, 15 Feb 1999 08:46:51 -0500 (EST)

> P.S.:
> One of the difficulties I had at first was in understanding the difference
> between super call and up-calls. A super call is a call to a super class
> (base class, lower down in the module hierarchy), an up-call is a call to a
> sub class (higher up in the module hierarchy). So: up-call = "sub call" (#
> super call).
> A framework like BlackBox heavily relies upon up-calls but tries to avoid
> super calls!
While the above statement may be technically correct, it mixes two
notions and thus confuses the issue even more.

A normal subroutine call is a "down call" since a procedure higher up
in the module chain is calling a procedure lower in the module chain.
With procedure variables and overridden methods, it becomes possible for
a module to invoke a procedure higher up in the module chain, or an "up
call". Such up calls are prevelant in framework systems, which are
unfinished by definition and comleted into a working system by
application specific procedures.

It is possible to discuss "up" and "down" calls without any reference to
object oriented programming.

Venkat Rao
Received on Mon Feb 15 1999 - 14:51:25 UTC

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