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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: Equality operator overloading in ADA 83
Date: 1997/05/02
Message-ID: <dewar.862576384@merv>#1/1
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References: <mheaney-ya023680002904972106200001@news.ni.net>
 <E9JMAM.L92.0.-s@inmet.camb.inmet.com>
Organization: New York University
Newsgroups: comp.lang.ada
Date: 1997-05-02T00:00:00+00:00
List-Id: <comp.lang.ada>


Tucker said

<<One suggestion which was made (a bit late) was to make a user-defined "="
on records the "official" "=" for the record type, and have the predefined
"=" never reemerge for records.  This is just expanding the current
rule for tagged records to apply to all record types.
Since things like "case" don't apply to record types, this imposes
essentially no additional burden on the implementation.>>

This sounds wrong (no additional burden). If you are using shared generics,
then this means that you *always* have to provide a thunk for record
equality for every record type, even in the (overwhelmingly common) case
where you don't do equality checking in any case in the body.

This causes extra overhead at runtime, which cannot be got rid of.

Thought: an interesting optimization in an Ada compiler would be to
recognize a tagged type that had no dispatching primitives (make any
primitives you have use 'Class), and then have the implementation
avoid generating a dispatch table in this case (perhaps you would
need a pragma to disable extensions as well).

Then you would be able to make equality compose without the extra overhead
of a tagged type at runtime ...

(I am talking here not of ideal language design considerations, but practical
considerations given Ada 95 as it is!)