Re: [Q] What does "*isa" stand for ?
Henrik Frystyk Nielsen (frystyk@w3.org)
Tue, 05 Mar 1996 20:38:44 -0500
Message-Id: <9603060138.AA04938@www20>
To: acs@aracnet.com
Cc: www-lib@w3.org
Subject: Re: [Q] What does "*isa" stand for ?
Date: Tue, 05 Mar 1996 20:38:44 -0500
From: Henrik Frystyk Nielsen <frystyk@w3.org>
acs@aracnet.com writes:
> In a structured stream class,
> what does the structure member "*isa" stand for ?
>
> as in:
> struct _HTStructured {
> CONST HTStructuredClass * isa;
> ....
> }
>
The isa element is the _only_ required part of a stream interface that
a stream has to provide. It is of type HTStreamClass which is defined in
HTStream.html. The isa element is an attempt to hide the fact that you
can't subclass as in C++, for example.
If no take a look at any of the stream implementations - or any function
using a stream - it use the methods pointed by the isa element.
It is a question whether the extra indirection going through the isa element
causes performance problems but the tests that I have performed using alpha's
profiler doesn't give this impression.
Henrik