Version 1.1 of ai22s/ai22-0015-1.txt

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!standard 3.9(26.1/3)          21-11-12 AI22-0015-1/01
!standard 3.10.2(14/3)
!standard 7.6.1(11.3/3)
!standard 7.6.1(11.4/3)
!class binding interpretation 21-11-12
!status work item 21-11-12
!status received 21-04-28
!priority Low
!difficulty Easy
!qualifier Clarification
!subject Innermost master of the call is ambiguous
!summary
Ambiguous wording is clarified.
!question
The phrase "innermost master of the call" as used in 3.10.2(14/3) is somewhat ambiguous, as it could mean "master of the function call" which has its own definition, or "innermost master that evaluated the call" which depends on the general definition of "master". Should we replace any such ambiguous phrases with a more explicit phrase? (Yes.)
!recommendation
Here are the potentially ambiguous uses we have identified:
3.9(26.1/3): Internal_Tag should return the tag of a type, if one exists, whose innermost master is a master of the point of the function call.
3.10.2(14/3): ... For an anonymous allocator defining the value of an access parameter, the accessibility level is that of the innermost master of the call. ...
7.6.1(11.3/3): For the type of an access parameter, the call that contains the allocator.
7.6.1(11.4/3): For the type of an access result, within the master of the call (see 3.10.2).
We propose that each of these be reworded to be explicit about whether we are talking about the master that evaluated the function call, or the "master of the function call" as defined in 3.10.2.
!wording
Modify 3.9(26.1/3):
Internal_Tag should return the tag of a type, if one exists, whose innermost master is a master of the point of {evaluation of} the function call.
Modify 3.10.2(14/3):
... For an anonymous allocator defining the value of an access parameter, the accessibility level is that of the innermost master of {the evaluation of} the call. ...
Modify 7.6.1(11.3/3):
For the type of an access parameter, {the evaluation of} the call that contains the allocator.
Modify 7.6.1(11.4/3):
For the type of an access result, within the master of the {function} call (see 3.10.2).
!discussion
We have added "the evaluation of" in three of the ambiguous places, and added "function" in the one place that is intended to be a reference to the phrase "master of the function call."
One could argue that in cases where the master of the function call is not the same as the innermost master that evaluated the call, this should have an effect on what is the master for an anonymous allocator of an access parameter, to be more consistent with the rules for aliased parameters. But anonymous allocators are generally frowned upon in various circles, so suggesting such a change would probably not be popular. Efforts to move away from run-time accessibility checks argue for replacing access parameters with aliased parameters, so such allocators would hopefully become even less common.
!ACATS test
No ACATS tests should be needed, as this is only clarifying existing wording, no change is intended.
!appendix

From: Tucker Taft
Sent: Friday, June 25, 2021  6:25 AM

An AdaCore engineer bumped into a confusing phrase in 3.10.2(14/3) where we
use "innermost master of the call" as a shorthand for "innermost master that
evaluated the call."  This shorthand predates the definition of the term
"master of the function call" but can now be seen as potentially confusing.
It could be interpreted as "innermost master of the function call" which
might be interpreted as essentially the same as "master of the function call."
So I would suggest we expand any uses of the shorthand "master of the call" to
either "master of the function call" or "master that evaluated the call" as
appropriate to the context, to avoid any such confusion.

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From: Tullio Vardanega
Sent: Friday, June 25, 2021  7:41 AM

Seems useful and opportune to me.

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