XCMD Limitations

[Ben Rubinstein]

Thanks to Richard and Brian (and Jim off-list) for replying.

In the meantime Kevin Miller confirmed that the supported list of callbacks
is defined as the 1.2 spec, and the magic of google (after I'd searched a
huge box with 10 years of Apple Developer CDs - apparently I didn't keep
them going back far enough!) located an old copy of the glue.  I've now
implemented some headers to switch out the newer calls, recoded the ones
that were needed, the external is working fine.

But I'm still confused as to which of the HC callbacks are supported.  The
1.2 spec that I found lists 27.  Of these, only 11 are in the MetaCard
"XCmdGlue.h" - but I know that my external is using at least some of the
others, eg ZeroToPas.  Perhaps Scott wishes to deprecate the others in
externals written specifically for MC/Rev - fair enough.  But that still
leaves anyone with an existing external to modify (possibly to make
cross-compatible with MC and HC) somewhat in the dark.  So I still think it
would be nice to

    a) get a definitive list of the HC compatible callbacks that are
supported, in addition to the MC-specific ones

    b) if the engine handled an unsupported callback more gracefully.


Just as background, since a number of people suggested this shouldn't be
necessary.  The situation is that we've got a project doing an upgrade to a
system we created some years ago.  One part that needs modification is a
HyperCard stack that does a huge data munge every month or so, taking some
4-6 hours in total.  I proposed moving this stack into MC (actually Rev)
first, and the upgrade on that version; on the basis of speed, better
ongoing support, etc.  The problem is that there is of course a limited
budget and some outcomes in terms of new functionaliy that have to be
achieved; and the transition obviously has risk factors.  I therefore
negotiated a strictly capped budget to attempt the transition; if I can't
prove that all problems have been solved by the time I've spent that, we're
just going to stick to making changes to the existing system.  Unfortunately
because of the lack of information (= my lack of knowledge) about exactly
what should work in the XFCN, and the fact that when an unsupported call was
made the entire machine froze, so that the process of investigation was
incredibly drawn out, I've blown a lot of the budget just getting past this
particular hurdle.

thanks again to all who helped,

  Ben Rubinstein               |  Email: benr_mc at cogapp.com
  Cognitive Applications Ltd   |  Phone: +44 (0)1273-821600
  http://www.cogapp.com        |  Fax  : +44 (0)1273-728866