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From: MCGUIRE@GRIN2.BITNET
Newsgroups: comp.os.vms
Subject: RE: Are Transfer Vectors Truly Useful When Creating Shareable Images?
Message-ID: <8707281945.AA02228@ucbvax.Berkeley.EDU>
Date: Mon, 27-Jul-87 14:16:00 EDT
Article-I.D.: ucbvax.8707281945.AA02228
Posted: Mon Jul 27 14:16:00 1987
Date-Received: Thu, 30-Jul-87 01:34:14 EDT
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> Date:         25 Jul 87 16:34:27 GMT
> From:         Bengt Baeverman 
> Subject:      Re: Are Transfer Vectors Truly Useful When Creating Shareable
>               Images?
>
> The easiest thing I can think of is using a vector, just like the transfer
> vector, to access the data. All the UNIVERSAL symbols are really pointers to
> the symbols you want to access.

In fact, you can even maintain compatibility if the data types change, if you
point to a descriptor instead of a data object.  For example, if you decide to
change a word to a longword in your shareable code, you can maintain backward
compatibility by supporting word arguments as long as you like, even while
writing new applications that pass longwords.  Of course, this requires you
to perform conditional branches and conversions based on the data type in the
descriptor.

Ed McGuire
Systems Coordinator
Grinnell College
MCGUIRE@GRIN2.BITNET