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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Ada202X: Easy to use "UML private"-like components
Date: Mon, 24 Jun 2013 15:20:05 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2013-06-24T15:20:05-05:00
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"Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message 
news:wccr4ftko44.fsf@shell01.TheWorld.com...
> Niklas Holsti <niklas.holsti@tidorum.invalid> writes:
>
>> Maybe my post was unclear: I tried to contradict Bob Duff's recollection
>> that an opaque type in Modula-2 is more like an Ada private type than
>> like an "stt access type". I think that a Modula-2 opaque type is very
>> similar to an "stt access type". Do you agree with me?
>
> Yes, given your quotes from Wirth, I agree that Modula-2 opaque types
> are much like stt access types.  I had remembered the restriction
> differently:  the type was required to fit in the size of a pointer,
> which included integers and enums and small records.  Probably the
> Modula-2 compiler I used had a nonstandard extension -- or else I am
> misremembering.

My recollection matches yours, Bob. Perhaps the rule was changed in later 
versions of the language. In any case, the Modula-2 obaque type is *not* a 
pointer type, so in that sense it is much more like an Ada private type than 
an access type of any sort. (I.e., I don't buy this analogy, especially as 
there isn't any such thing as an stt-access-type -- the operative thing is 
an stt-incomplete-type, which is nothing like a Modula-2 opaque type. The 
access type is completely normal, its the designated object that's special.)

                              Randy.