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From: PATTIS@WARD.CS.WASHINGTON.EDU (Richard Pattis)
Newsgroups: net.lang.mod2
Subject: Should all opaque types be pointers? No.
Message-ID: <12248635590.12.PATTIS@WARD.CS.WASHINGTON.EDU>
Date: Tue, 21-Oct-86 16:04:50 EDT
Article-I.D.: WARD.12248635590.12.PATTIS
Posted: Tue Oct 21 16:04:50 1986
Date-Received: Wed, 22-Oct-86 06:14:28 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 15


  I would like to complain about opaque types being pointers only. When I teach
ADTs, I teach a Table, with a few operations that manipulate cursors (a unifi-
cation of indexes and pointers).  One can locate an element and get a cursor;
one can use the cursor to retrieve/update information from/to a table.  The
definition module of the Table ADT exports opaquely the cursor type.  One
implementation of Table uses arrays, where the cursor type is integer.  Another
implementation uses pointers for cursors.

  This example will be impossible with the new standard.  Couldn't one say
that opaque types must allow for the largest of all the primitive (so called,
one-word) types?  What is the rationale for restricting it to pointers only?

Rich
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