From jkr@jkr.cc.rl.ac.uk Wed Feb 28 16:57:37 2001 Received: from nameserv.rl.ac.uk (nameserv.rl.ac.uk [130.246.135.129]) by dkuug.dk (8.9.2/8.9.2) with ESMTP id QAA24111 for ; Wed, 28 Feb 2001 16:57:36 +0100 (CET) (envelope-from jkr@jkr.cc.rl.ac.uk) Received: from jkr.cc.rl.ac.uk (jkr.cc.rl.ac.uk [130.246.8.20]) by nameserv.rl.ac.uk (8.8.8/8.8.8) with ESMTP id PAA30830 for ; Wed, 28 Feb 2001 15:57:30 GMT Received: (from jkr@localhost) by jkr.cc.rl.ac.uk (8.8.8+Sun/8.8.8) id PAA26509 for SC22WG5@dkuug.dk; Wed, 28 Feb 2001 15:59:20 GMT Date: Wed, 28 Feb 2001 15:59:20 GMT From: John Reid Message-Id: <200102281559.PAA26509@jkr.cc.rl.ac.uk> To: SC22WG5@dkuug.dk Subject: Iterpretation 31 (pointer function as actual argument): draft response MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Dear WG5, Here is my next draft interpretation response. This is not a new one. It failed its J3 ballot, but there were 11 YES votes to 5 NO votes. The ballot comments are in 00-329 and are appended for your convenience. There is no question that the text of the standard needs to be edited. I have added an edit without altering the conclusion. I would appreciate comments before I send it to J3, preferably to me in private. Cheers, John. .................................................. NUMBER: 000031 TITLE: Association of pointer function result with INTENT(OUT) dummy argument KEYWORDS: Pointer association, dummy argument association, intent attribute DEFECT TYPE: Clarification STATUS: J3 consideration in progress QUESTION: Consider the following program. PROGRAM P INTEGER, TARGET :: T CALL SUB(FPTR()) CONTAINS FUNCTION FPTR() INTEGER, POINTER :: FPTR FPTR => T END FUNCTION FPTR SUBROUTINE SUB(IO) INTEGER, INTENT(OUT) :: IO IO = 17 END SUBROUTINE SUB END PROGRAM P According to 12.4.1 [200:30-32], "If a dummy argument is not a pointer and the corresponding actual argument is a pointer, the actual argument shall be currently associated with a target and the dummy argument becomes argument associated with that target." According to 12.4.1 [201:19-21], "If a dummy argument has INTENT(OUT) or INTENT(INOUT), the actual argument shall be definable." According to 5.1.2.3 [53:29-31], "The INTENT(OUT) attribute specifies that. . . any actual argument that becomes associated with such a dummy argument shall be definable." The definition of "definable" supplied in Annex A (the term does not appear to be defined in normative text) is: "A variable is <> if its value may be changed by the appearance of its or on the left of an ." According to this definition, "definable" is a property of variables only. In the example above, the actual argument is not a variable. However, the actual argument is pointer associated with an object that is definable. The text cited from 5.1.2.3 refers to the "actual argument that becomes associated with the dummy argument", but the first piece of text cited from 12.4.1 makes it clear that when the actual argument is a pointer, it is the target with which it is associated that becomes argument associated with the dummy argument, and not the actual argument itself. Was it the intent of the committee that this program should not be standard-conforming? ANSWER: No, it was not intended that this program be standard conforming. Unfortunately, the standard does not specify whether an expression that is not a variable is definable. It was not intended that it be definable since it is not permitted on the left-hand side of an assignment statement (7.5.1.1) or in a nullify statement (6.3.2). An edit makes this clear. Given this edit, the text quoted above from page 53 leads to the conclusion that the program does not conform to the standard. It would still not conform if the intent declaration were removed since 12.5.2.2 contains the text A dummy data object whose intent is not specified is subject to the limitations of the data entity that is the associated actual argument. That is, a reference to the dummy data object may occur if the actual argument is defined and the dummy data object may be defined if the actual argument is definable. EDIT: On page 16, add to the end of the paragraph that is subclause 2.4.3.2 [16:37] 'An expresion is not definable unless it is a variable.' SUBMITTED BY: Henry Zongaro HISTORY: 98-177 m146 Submitted WG5/N1414 Draft answer 00-260 m154 Passed by J3 meeting 00-329 m155 Failed J3 letter ballot .................................................. RichB's NO vote on 000031 See IBM's comments. Malcolm's YES comment on 000031 I disagree with the other comments that the dummy argument is argument-associated with something that is not an actual argument. The dummy argument is associated with the (value of) the actual argument expression. Craig's NO vote on 000031 I agree with Van's comments. Kurt's NO vote on 000031 I agree with Van. The pointer that is the function result is not definable, but the target identified by that pointer (in this case, T) _is_ definable. In the example given, the dummy argument is associated with the target, not the pointer. [The prohibition against a function reference appearing on the left hand side of an assignment statement is syntactic in nature and has no bearing on this semantic question.] Van's NO vote on 000031 I don't know the intent of the committee, but my experience in reading the standard is that the area of argument association of pointers is murky. It is my preference that a non-pointer dummy argument is considered to be associated with a definable actual argument if the actual argument is a pointer that is associated with a definable target. The glossary entry for "definable" is not normative, and, like Henry, I could not find a normative definition for it. I prefer not to depend on non-normative text to resolve an interpretation. Henry's arguments concerning the relation between the passages he cites from 5.1.2.3 and 12.4.1 convince me that the example he provides should be standard-conforming. If the dummy argument had the pointer attribute, I would accept a conclusion that its pointer association status could not be changed, because in that case, the actual argument would be a function result. Henry's NO vote on 000031 We are inclined to agree with Van Snyder on this question. It is clear that the standard treats specially pointers that appear as actual arguments when the associated dummy is not a pointer: the dummy becomes argument associated with the target of the pointer, not with the actual argument itself. We agree the actual argument is not definable, but that seems irrelevant because the entity that is argument associated with the target is not the actual argument in this case. It seems far more likely that the drafters of the standard failed to take into account the case of a pointer actual argument that corresponds to a nonpointer dummy argument when they required that the "actual argument shall be definable" in [201:19-21] and [53:29-31]. In fact, the text cited at 5.1.2.3 [53:29-31] is particularly troublesome. To repeat, it states that: The INTENT(OUT) attribute specifies that. . . any actual argument that becomes associated with such a dummy argument shall be definable. But in the case of a pointer actual argument that corresponds to a nonpointer dummy, there is no actual argument associated with the dummy. The target of the pointer is associated with the dummy, but the target is not the actual argument. We also feel that a normative definition of the term "definable" is required.