08-172
To: J3
From: Malcolm Cohen
Subject: Interp F95/0074
Date: 2008 May 09

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NUMBER: F95/0074
TITLE: TARGET dummy arguments and POINTER expressions
KEYWORDS: TARGET, POINTER, dummy arguments
DEFECT TYPE: Interpretation
STATUS: J3 consideration in progress
        see also F95 interp 000031

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.  5.1.2.7 states
    "If no INTENT attribute is specified for a dummy argument, its use
     is subject to the limitations of the associated actual argument."
   The associated actual argument is the function reference f(x); this
   is an expression, not a variable, and therefore not definable,
   because only variables can be defined (in the sense of being given
   a value, see 2.4.3.1.1 and 2.5.5).

2. The call to s2 is not standard conforming. 12.4.1.2 says:
     "If a nonpointer dummy argument has INTENT(OUT) or INTENT(INOUT),
      the actual argument shall be definable."
   Again the actual argument is a function reference, 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
   12.4.1.2, which says [270:5-0]
     "If the dummy argument has the TARGET attribute, does not have
      the VALUE attribute, and is either a scalar or an assumed-shape
      array, and the corresponding actual argument has the TARGET
      attribute but is not an array section with a vector subscript
      then
        (1) Any pointers associated with the actual argument become
            associated with the corresponding dummy argument on
            invocation of the procedure ..."

EDITS: None.

SUBMITTED BY:  Malcolm Cohen

HISTORY: 99-198      m150   F95/0074 submitted
         WG5/N1414          Draft answer
         00-260      m154   Passed by J3 meeting
         00-329      m155   Failed J3 letter ballot
         04-311      m168   Passed by J3 meeting vote - alternate
                             answer removed
         04-417r1    M170   Passed by J3 letter ballot #8
         05-180      m172   Failed WG5 ballot N1617
         08-172      m184   Revised answer

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