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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Ada202X: Easy to use "UML private"-like components
Date: Sat, 22 Jun 2013 19:41:00 +0300
Organization: Tidorum Ltd
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Date: 2013-06-22T19:41:00+03:00
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On 13-06-21 21:36 , Robert A Duff wrote:

> I share your disdain for what you called "opaque" types -- it forces you
> into heap management, which leads to extra trouble.  But I object to
> calling them "opaque" types.  Ada folks usually call them "stt access
> types" and "stt incomplete types", or "Taft amendment types", because
> they were invented by Tucker Taft and added to Ada 83 at the last minute
> when nobody realized all the headaches they cause for compiler writers.
> The term "opaque type" comes from Modula-2, IIRC, and is more like
> an Ada private type, with some annoying restrictions added.

According to the Modula-2 Reference at
http://www.modula2.org/reference/modules.php, when a Modula-2 definition
module declares an opaque type,

"The corresponding implementation module must contain a full type
declaration for any opaque types declared in the definition module.  The
full type declaration must define a pointer type."

I take this to mean that a Modula-2 opaque type uses indirection through
a pointer type, just as the "stt access types" in Ada, and unlike Ada
private types in general.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
      .      @       .