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From: ytomino <aghia05@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: discriminant questions
Date: Tue, 20 Sep 2011 14:39:07 -0700 (PDT)
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Date: 2011-09-20T14:39:07-07:00
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Thank you for your suggestion. I'm reading AARM now...

For the first time, I got to know the difference between "access
discriminant" and a normal discriminant having named access type.
I am surprised at that a normal discriminant having named access type
can have default and is able to assignment.
But, in RM 4.1 (5 (2/3)), "This aspect is specified by a name that
denotes an access discriminant declared for the type T."...It seems
that a normal discriminant having named access type can not be
Implicit_Dereferene...
Close! It's regrettable.

Back to the subject, lifetime of coextension, It's interesting.
Coextension probably is one of the reason that objects with access
discriminant can never allow them to be changed.
However, I have not resulted in firm belief yet.

As another reason, default of "access discriminant" has been used for
discriminating which a formal limited type in generic is
really(immutably) limited or non-limited since Ada 95.
"immutably limited" concept is used widely. (Therefore it is hard to
change this rule.)

Is my understanding right...?

I have not been found the reason about accessibility check yet.
I'm going to read RM 3.10.2 and AI95-00230-01 at next.