J3/04-311

To: J3
From: Malcolm Cohen
Subject: Interp F90/000074
Date: 5th May 2004

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NUMBER: 000074
TITLE: TARGET dummy arguments and POINTER expressions
KEYWORDS: TARGET, POINTER, dummy arguments
DEFECT TYPE:
STATUS: J3 consideration in progress

QUESTION:

Consider the following program.

PROGRAM questionable
  REAL,TARGET :: x
  CALL s1(f(x))
  CALL s2(f(x))
  CALL s3(f(x))
CONTAINS
  FUNCTION f(a)
    REAL,POINTER :: f
    REAL,TARGET :: a
    f => a
  END FUNCTION
  SUBROUTINE s1(variable)
    variable = 42                  ! statement 1
  END SUBROUTINE
  SUBROUTINE s2(variable)
    INTENT(OUT) variable
    variable = 42                  ! statement 2
  END SUBROUTINE
  SUBROUTINE s3(targ)
    REAL,TARGET :: targ
    REAL,POINTER :: p
    p => targ
    PRINT *,ASSOCIATED(p,x)        ! statement 3
  END SUBROUTINE
END

Is this program standard-conforming, and if so, what value is
printed?

The real question is whether an expression argument that is a pointer
function reference is treated as a variable (data-object) argument
with the variable being the target of the pointer expression.  (Or
whether it is dereferenced as usual in the absence of POINTER dummy
arguments).

Re (statement 1), the question is whether VARIABLE is definable when
argument-associated with "F()".

Re (statement 2), if the previous answer was Yes (VARIABLE is
definable), then presumably it can be made INTENT(OUT).  A random
sample of 4 compilers revealed that they considered it not to be
definable.

Re (statement 3), the question is whether P is pointer-associated
with X, not pointer-associated with X, or processor-dependent.  Of
the same random sample 3 thought it was associated with X, 1 thought
not.

ANSWER:

1. The call to s1 is not standard conforming. 12.5.2.1 says:

'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.'

Here the actual argument is a function result, which is not
definable.  For example, it is not permitted on the left-hand side
of an assignment statement, since it is not a variable.  (Being
"defined" or "undefined" is fundamentally a concept that applies only
to variables.)

2. The call to s2 is not standard conforming. 12.4.1.1 says:

'If a dummy argument has INTENT(OUT) or INTENT(INOUT), the actual
argument shall be definable.'

Again the actual argument is a function result, which is not
definable.

3. The call to s3 is standard conforming and the pointer assignment
in s3 causes p and x to become associated. This may be deduced from
12.4.1.1, which says [200:38-42]:

'If the dummy argument has the TARGET attribute and is either scalar
or is an assumed-shape array, and the corresponding actual argument
has the TARGET attribute but is not an array section with a vector
subscript (1) Any pointers associated with the actual argument become
associated with the corresponding dummy argument on invocation of the
procedure ...'

EDITS: None.

ALTERNATIVE ANSWER:

The program was intended to be standard conforming.  Edits are
supplied to move the requirement for definability from the actual
argument (which in the examples is a pointer function reference) to
the data entity with which the dummy argument is associated (which in
the examples is a variable).

ALTERNATIVE EDITS:

[53:30-31] Change "actual argument that becomes associated"
to "data entity that becomes argument associated".
[53:35-36] Ditto.
{Repair INTENT attribute description.}

[201:19-20] Change "the actual argument shall be definable"
to "it shall be argument associated with a definable data object."
[201:20-21] Change"the corresponding actual argument"
to "the data entity with which it is argument associated".
{Repair requirements for explicit INTENT.}

[206:28-29] Change "that is the associated actual argument"
to "with which it is argument associated".
[206:29-30] Change "the actual argument"
to "its associated data entity" twice.
{Repair requirements for unspecified INTENT.}

SUBMITTED BY:  Malcolm Cohen
HISTORY: 99-198      m150   submitted
         WG5/N1414          Draft answer
         00-260      m154   Passed by J3 meeting
         00-329      m155   Failed J3 letter ballot
         04-311      m168   Revised with alternative
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