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From: brnstnd@kramden.acf.nyu.edu (Dan Bernstein)
Newsgroups: comp.lang.misc
Subject: Technical: Definitions of ``Poynter'', ``Shyfting''
Message-ID: <19485:Nov1608:33:4490@kramden.acf.nyu.edu>
Date: 16 Nov 90 08:33:44 GMT
Sender: brnstnd@kramden.acf.nyu.edu (Dan Bernstein)
Organization: IR
Lines: 25

Please include technical content, and only technical content, in any
followup to an article whose subject begins with ``Technical:''. Change
the subject line to introduce nontechnical issues. I will obey this rule
religiously. Note that emotional issues can be technical (e.g., whether
alias or noalias is more natural), but personal attacks cannot.

Here are definitions of two terms.

Poynter: An object that can hold the address of another object (perhaps
of a restricted type). As usual, a poynter supports assignment and
comparison. It may be set to the ``address of'' an object. It may be
``dereferenced'' in order to evaluate or modify the object whose address
it holds. These operations are explicit.

Shyfting: The operation of re-indexing a reference to an array with a
different base, so as to produce a reference to the same object with the
new indices.

A C pointer is a poynter with shyfting. A machine language index is a
poynter with shyfting. A Pascal or Ada pointer is a poynter without
support for shyfting. Apparently the new Fortran includes shyfting
separately from its poynters. Ada's slicing is a limited form of
shyfting.

---Dan