Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!husc6!cmcl2!acf5!sabbagh
From: sabbagh@acf5.NYU.EDU (sabbagh)
Newsgroups: comp.sys.mac.programmer
Subject: Re: HandleObject vs. 5+ meg of RAM and Virtual Memory
Message-ID: <1220@acf5.NYU.EDU>
Date: 18 Aug 90 17:55:48 GMT
References: <279@unf7.UUCP>
Reply-To: sabbagh@acf5.UUCP ()
Organization: New York University
Lines: 57

In article <279@unf7.UUCP> shite@unf7.UUCP (Stephen Hite) writes:
>
>   If I have 5 or 8 meg of RAM and virtual memory (a.k.a System 7.0.2 :-))
>is it really *worth* the limitations of using HandleObject?  Some of limitations
>are (as taken from the MPW C++ Beta Manual):
>
>   1. You can't "...declare global variables, local variables, arrays, members,
>      or parameters of handle-based types (rather than pointers to them)."
>
>   2. You can't use multiple inheritance (as discussed previously ad nauseum).
>
>   3. "It is not possible to allocate an array of handle-based objects, for
>      example, new MyObjects[10]."
>
>   4. You cannot "...take a pointer to a field of an indirect class (i.e.,
>      &x->y).  This restriction includes the implicit use of pointers by ref-
>      erences, such as int& p = x->y."
>
>   [stuff deleted].

More thought would have revealed that these restrictions are quite reasonable.
What is a HandleObject?  It is an object that is intended to be allocated from
the Mac heap! These are referenced using handles, which allows the Memory 
manager to deal with fragmentation, etc.

Suppose you were writing code in C, Pascal, or any other language besides C++.  Can you allocate handle objects as global or local variables, arrays, members
or parameters of handle-based objects? NO, you can only manipulate pointers
to them!  Can you allocate an array of handle-based objects?  No, you would
need an array of handles to point to them (which you CAN do).

Basically, HandleObject alleviates you from dealing with 1) dereferencing
issues when dealing with the heap and 2) knowing which Toolbox calls move
memory.

So, my $0.02:

1) Use HandleObjects for things you would ordinarily allocate from the heap
in another language.  It will alleviate a number of programming issues
unique to the Macintosh.

2) Don't use HandleObjects for things you would want as variables, array
items, etc.  I wouldn't make a Point class a HandleObject.  Note that
you can still use the heap for these other object classes, but you have
to manage them yourself.


Hadil G. Sabbagh
E-mail:		sabbagh@csd27.nyu.edu
Voice:		(212) 998-3125
Snail:		Courant Institute of Math. Sci.
		251 Mercer St.
		New York,NY 10012

"'He was killed by the usual cabal: by himself, first of all; by the woman
  he knew; by the woman he did not know; by the man who granted his inmost
  wish; and by the inevitable fifth, who was keeper of his conscience and
  keeper of the stone.'"	-R. Davies, "Fifth Business"