From: ncohen@watson.ibm.com (Norman H. Cohen)
Subject: Re: Record aggregate question (language lawyer needed!)
Date: 1996/06/21
Date: 1996-06-21T00:00:00+00:00 [thread overview]
Message-ID: <4qf5el$1633@watnews1.watson.ibm.com> (raw)
In-Reply-To: mcriley.835361851@BIX.com
In article <mcriley.835361851@BIX.com>, mcriley@BIX.com (mcriley on BIX) writes:
|>
|> The following test program is accepted without question by one Ada
|> compiler and executes without any qualms, while another warns of
|> a constraint_error at runtime. Which is correct, or, is the exact
|> implementation left up to the compiler implementor?
|>
|> procedure Rec_Test is
|>
|> type Task_Record_Type is
|> record
|> Originator : String (1 .. 20);
|> Header_Dtg : String (1 .. 12);
|> end record;
|>
|> Task_Record : Task_Record_Type := (others => (others => ' '));
|>
|> begin
|> null;
|> end rec_test;
|>
|> The relevant part of the LRM is 4.3.1[1]: "A component association
|> with the choice others [...] is only allowed if the represented
|> components are all of the same type." Well the components are
|> both of the same _type_, but obviously the subtype constraints vary.
Since you quote the Ada-83 RM, Ada-83 AI-00244 applies. The summary of
that AI is:
In a record aggregate, a component association having multiple choices
denoting components of the same type is considered equivalent to a
sequence of single choice component associations representing the same
components.
Thus, what you have written is equivalent to
Task_Record: Task_Record_Type :=
(Originator => (others => ' '),
Header_Dtg => (others => ' ') );
It should work without problem. Perhaps the compiler that raises
Constraint_Error (or threatens to) predates AI-00244, which received
final approval in November 1986.
The URL for the full text of AI83-00244 is:
ftp://sw-eng.falls-church.va.us/public/AdaIC/standards/83com/ai-00244-bi.wj
(By the way, the Ada-95 equivalent of the rule in RM83-4.3.1(1) is in the
last sentence of RM95-4.3.1(16). The effect of AI83-00244 is captured in
RM95-4.3.1(20).)
--
Norman H. Cohen ncohen@watson.ibm.com
next prev parent reply other threads:[~1996-06-21 0:00 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
1996-06-21 0:00 Record aggregate question (language lawyer needed!) mcriley on BIX
1996-06-21 0:00 ` Norman H. Cohen [this message]
1996-06-21 0:00 ` Theodore E. Dennison
1996-06-22 0:00 ` Robert A Duff
1996-06-24 0:00 ` Norman H. Cohen
1996-06-24 0:00 ` Philip Brashear
1996-06-25 0:00 ` Theodore E. Dennison
1996-06-21 0:00 ` Robert A Duff
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