To:      J3                                                     07-338
From:    Van Snyder
Subject: Referencing deferred binding via absent dummy argument
Date: 2007 November 15

NUMBER: F03/0109
TITLE: Referencing deferred binding via absent dummy argument
KEYWORDS: Type-bound procedure, deferred binding
DEFECT TYPE: Erratum
STATUS: J3 consideration in progress

QUESTION:

The intent was that it would be impossible to reference a deferred
binding.  However, it doesn't appear to me that this intent was achieved.
Consider the following program

  program P
    type, abstract :: T
    contains
      procedure(sub), nopass, deferred :: deferred_proc
    end type T

    call sub

  contains

    subroutine Sub ( X )
      class(t), optional :: X
      call x%deferred_proc
    end subroutine Sub

  end program P

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

Since x%deferred_proc has the NOPASS attribute, this does not require the
value of x (4.5.7) and thus is not a reference to x (2.5.6).  Therefore,
the first item in the second list in 12.4.1.2 (at [04-007:272:32-33]) does
not prohibit this.

ANSWER:

This was not intended to be a valid program. A type-bound procedure shall
not be invoked through an absent dummy argument. An edit is supplied to
clarify this situation.

EDITS:

Insert after C1224 in subclause 12.4 (at [04-007: 266: 24]) ([07-007r3:
309: 11]):

"The <data-ref> shall not be an undefined pointer, a disassociated
pointer, an unallocated allocatable variable, or a dummy data object that
is not present (12.4.1.6)." (This subsumes the edits for F03/0003 and
F03/0004).

SUBMITTED BY: Van Snyder

HISTORY: 07-xxx    m182  F03/0109 Submitted