May 16 00:54 1996  X3J3/96-098R1 (2 Pages) Page 1


                                                               X3J3/96-098R1

     To: X3J3
     From: Richard Maine
     Subject: Intent for Pointer Arguments

     Jor item 58 requests a "regularization of the handling of pointer
     arguments."  The primary change suggested is to allow the
     specification of INTENT for pointer arguments; the other suggestions
     all depend on this.  This Jor item was identified by the U.S. in
     August 1995 as a medium priority requirement for f2k.  Jor item
     65 is also essentially equivalent.

     WG5 repository item 44 corresponds to this Jor item and is
     supplemented by WG5 repository item 44a, which simillarly requests the
     specification of INTENT for pointer arguments.

     This paper is a proposal for a detailed specification of this feature.

     1. A pointer dummy argument may be specified to have an INTENT.
        As with non-pointer arguments, the INTENT may be specified as
        IN, OUT, or INOUT, or it may be left unspecified.

     2. The specification of INTENT relates only to the association
        of the pointer, not to the value of the target.

        Rationale:

          As both repository items 44 and 44a note, there seems little
          useful functionality in most other choices.  If the association
          of the pointer can change during execution of the procedure, then
          it makes little sense to talk about the INTENT of the target(s).

          If the pointer has INTENT(IN), then there do seem to be
          two useful possibilities.  You might want to allow or disallow
          changing the value of the target during execution of the procedure.
          WG5 item 44a suggests that these possibilities are covered by
          making the dummy argument a non-pointer, but I am not entirely
          convinced.  Making the dummy argument a non-pointer would disallow
          such things as testing its association status; for example, it
          is not allowed to have a disassociated pointer as an actual
          argument for a dummy non-pointer argument.

          A straw vote of x3j3 favored the approach suggested in the
          repository, where the INTENT applies solely to the pointer
          association.

        End rationale

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     3. The INTENT of a dummy pointer limits the way in which the dummy
        can be used in the subprogram.  These limitations closely
        parallel those currently specified in 12.5.2.1 of the f95 dis.

        3a. If a dummy pointer has INTENT(IN), its association may not
            be changed during execution of a procedure.

        3b. If a dummy pointer has INTENT(OUT), it is initially
            disassociated on entry into the procedure.

        3c. If a dummy pointer has no INTENT specified, its association
            may be changed only if the actual argument is a pointer
            variable.

     4. The INTENT of a dummy pointer limits the nature of the actual
        arguments that can be associated with the dummy.  These
        limitations closely follow those currently specified in section
        12.4.1 for non-pointer arguments.

        There are only two possible forms for an actual argument
        corresponding to a dummy pointer argument.  The actual
        argument may be a pointer variable or it may be a pointer
        function invocation.

        4a. If a dummy pointer has INTENT(OUT) or INTENT(INOUT), then
            the actual argument must be a pointer variable.

        4b. If a dummy pointer has unspecified INTENT, then the actual
            argument must be a pointer variable if the association of
            the dummy argument is redefined.

        4c. If the dummy pointer has INTENT(IN), then there are no extra
            restrictions on the allowable actual arguments.

     5. A few other places clearly need some edits, but they seem almost
        mechanical.  For example,

        5a.  Section 5.1.2.3 pretty much says the same kinds of things as
             sections 12.5.2.1 and 12.4.1.  Presumably we would like these
             sections to continue to roughly agree.

        5b.  The document needs a global search for INTENT to do the
             actual edits, but we don't yet need that at this stage.

     Note that allowing pointer dummy arguments to have specified INTENT
     automatically has the effect of allowing defined operators on
     pointer operands as requested in Jor item 65.  There is no explicit
     prohibition of defined operations with pointer operands; they were
     disallowed indirectly because defined operators require dummy
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     arguments with specified intents.  An example of a defined operation
     on pointers should be included when the edits are made.  We will
     also need to search to make sure that we find and remove any
     mentions of the former indirect disallowance of such defined
     operations.

     Note also that although you can have defined operations with
     pointer dummy arguments, the pointer attribute cannot be used
     for disambiguation.