Version 1.4 of ai22s/ai22-0008-1.txt

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!standard 4.3.3(14.1/5) 22-02-03 AI22-0008-1/03
!class binding interpretation 21-11-11
!status Corrigendum 1-2022 22-02-03
!status WG9 Approved 22-10-18
!status ARG Approved 16-0-0 22-02-03
!status work item 21-11-11
!status received 21-11-09
!priority Low
!difficulty Easy
!qualifier Omission
!subject Nominal subtype of a delta aggregate

!summary

We talk about an applicable index constraint rather than a nominal subtype for a delta aggregate. Specifically, the base expression of a delta aggregate has the same applicable index constraint as the delta aggregate as a whole.

!issue

4.3.3(14.1/5) says

For the base_expression of a delta_aggregate, if the nominal subtype of the delta_aggregate is a constrained array subtype, the applicable index constraint is the constraint of the subtype;

Does a delta aggregate have a nominal subtype? (No.)

!recommendation

(See Summary.)

!wording

Modify 4.3.3(14.1/5):

For the base_expression of a delta_aggregate[, if the nominal subtype of the delta_aggregate is a constrained array subtype], the applicable index constraint is [the constraint of the subtype] {that of the delta_aggregate as a whole, if any};

!discussion

Aggregates generally don't have nominal subtypes, so this bullet is reworded to avoid using that term.

!corrigendum 4.3.3(14.1/5)

Replace the paragraph:

For the base_expression of a delta_aggregate, if the nominal subtype of the delta_aggregate is a constrained array subtype, the applicable index constraint is the constraint of the subtype;

by:

For the base_expression of a delta_aggregate, the applicable index constraint is that of the delta_aggregate as a whole, if any;

!ACATS test

This rewording shouldn't change the needed ACATS test for this bullet.

!appendix


[Editor's note: From a private thread with many more topics in each message;
only the relevant part is given here.]

From: Jeff Cousins
Sent: Tuesday, November 9, 2021  3:16 AM

4.3.3(14.1/5) – the item being written to can have a nominal subtype, and 
maybe the item used as the base expression, but can the delta aggregate 
itself?

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From: Tucker Taft
Sent: Tuesday, November 9, 2021  9:18 AM

Not sure what you are asking here...

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From: Jeff Cousins
Sent: Tuesday, November 9, 2021  11:53 AM

4.3.3 (14.1/5) says “... if the nominal subtype of the delta_aggregate ...”

What is the nominal subtype  of a delta aggregate?  Taking the example from 
4.3.4 (27/5), where in the following is a subtype named (other than Integer)?

((0 => 1.0, 1 => 2.0, 2 => 3.0)
       with delta Integer(Random * 2.0) => 14.2)

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From: Tucker Taft
Sent: Tuesday, November 9, 2021  12:53 PM

This looks like a bug in the wording.  Aggregates generally don't have
"nominal" subtypes.  They are one of the few things that don't.
4.3.3(14.1/5) should probably say:

For the base_expression of a delta_aggregate[, if the nominal subtype of 
the delta_aggregate is a constrained array subtype], the applicable index
constraint is [the constraint of the subtype] {that of the delta_aggregate
as a whole, if any};
 
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