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From: paulr@syma.sussex.ac.uk (Paul Russell)
Newsgroups: comp.sys.mac.programmer
Subject: Unsafe use of an object field as a var or > 4 byte parameter
Message-ID: <4749@syma.sussex.ac.uk>
Date: 19 Mar 91 14:09:17 GMT
Sender: paulr@syma.sussex.ac.uk
Followup-To: comp.sys.mac.programmer
Organization: University of Sussex
Lines: 20

When passing a parameter such as a Str255 as a parameter
to a method, where the parameter is also an object field,
the MPW Pascal compiler complains:

### Pascal - Error 815 Unsafe use of an object field as a var or > 4 byte parameter

I can understand why it might object to a VAR parameter being
passed in this way, since that would in effect be dereferencing
a handle. But why should it object when the parameter is not
VAR ? For non-VAR parameters surely a local copy of the parameter
is made before the called function has a chance to move memory ?
Am I missing something here ? It's a real pain to have to keep
making temporary copies of object fields before passing them to
methods but I don't want to start putting {$H-} directives in the
code unless I know it really is safe.

(BTW - THINK Pascal doesn't care about this - does that mean that
it handles the problem for you, or that it just ignores it ? ;-))

//Paul