J3/04-323r1

Date:    10th August 2004
To:      J3
From:    Malcolm Cohen
Subject: Type-bound procedures and undefined association status

The following interp request from 04-323 has been modified to
(a) make the question valid
(b) propose two slightly different answers (straw vote?)

/INTERP subgroup recommends answer 1.

NUMBER:
TITLE: Type-bound procedures and undefined association status
KEYWORDS: Type-bound procedure, dynamic type
DEFECT TYPE: Erratum
STATUS: J3 consideration in progress

QUESTION:

It appears that the dynamic type is undefined for a pointer with
undefined association status.  This impacts type-bound
procedures. Consider the following program.

  program undefined

    type :: t
    contains
      procedure, nopass :: nondeferred_proc => sub
    end type t
    type, extends(t) :: t2
    contains
      procedure, nopass :: nondeferred_proc => sub2
    end type t2

    class(t), pointer :: x

    call x%nondeferred_proc

  contains
    subroutine sub
      write (*,*) 'Hello.'
    end subroutine sub
    subroutine sub2
      write (*,*) 'Goodbye.'
    end subroutine sub2
  end program defer

Is this a valid program?  If not, what restriction of the
standard does it violate?  If so, what does it print.

Note that x%nondeferred_proc does not require the value of x (4.5.7)
and thus is not a reference to x (2.5.6).  Therefore, [83:23-24]
does not prohibit this.

If x were disassociated, its dynamic type would be t and the
interpretation of this would be reasonably clear.

However, the standard does not appear to specify the dynamic type
of x when its association status is undefined.  Nor can I find
any prohibition that applies to this case.

ANSWER 1:

No, the program is not valid, because the standard does not establish
an interpretation of it.  An edit is supplied to clarify this.

Furthermore, the case with a disassociated pointer was not intended to
be valid.  An edit is supplied to correct this oversight.

ANSWER 2:

No, the program is not valid, because the standard does not establish
an interpretation of it.  An edit is supplied to clarify this.

DISCUSSION (for answer 1 only):

Access to object-bound procedures (a.k.a. procedure pointer
components) always require there to be an object.  Access to
type-bound procedures of an object was intended to require this too,
but the effect of the NOPASS attribute on this was overlooked.

EDITS 1:

[266:24+] Insert new constraint
"C1224a (R1219) If <data-ref> is a pointer, it shall be associated.
If <data-ref> is allocatable, it shall be allocated."

EDITS 2:

[266:24+] Insert new constraint
"C1224a (R1219) If <data-ref> is a pointer, it shall not have a
pointer association status of undefined."

SUBMITTED BY: Richard Maine

HISTORY: J3/04-323   m169 Submitted
         J3/04-323r1 m169 Revised, answer proposed.