10-157
To: J3
From: Robert Corbett
Subject: Interpretation Request: Deallocating argument associated
				 objects
Date: 2010 May 31

All Fortran 2008 references are with respect to J3/10-007.

QUESTION:

Can an object that was created by an ALLOCATE statement and that
is argument associated with a dummy argument be deallocated by a
DEALLOCATE statement through a variable other than the dummy
argument?

ANSWER:

No.

DISCUSSION:

Interpretations F90/000081 and F90/000125 provide background
information for this interpretation request.

Section 12.5.2.13, paragraph 1, page 300, lines 2-4 of
Fortran 2008 states

    While an entity is associated with a dummy argument, the
    following restrictions hold.

      (1)  Action that affects the allocation status of the
	   entity or subobject thereof shall be taken through
	   the dummy argument.

I read that statement as meaning that an allocated object cannot be
deallocated while it is associated with a dummy argument except
through the dummy argument.  I was recently told by members of the
committee that only allocatable variables have an allocation status,
and that therefore the restriction applies only to allocatable
variables.  I pointed out that Note 12.33 on pages 300-301
contradictions that assertion.  I was then told that Note 12.33 is
inaccurate.

Consider the following program

      SUBROUTINE SUBR(A)
        REAL A(*)
        REAL P, Q
        DIMENSION P(:), Q(:)
        POINTER P, Q
        COMMON P, Q

        DEALLOCATE (P)
      END

      PROGRAM MAIN
        REAL P, Q
        DIMENSION P(:), Q(:)
        POINTER P, Q
        COMMON P, Q

        ALLOCATE (P(100))
        P = 1.0
        Q => P
        CALL SUBR(Q(1:100:11))
      END

Under the interpretation that the restriction cited above applies only
to allocatable variables, this program is standard conforming.  Every
compiler I checked implements the CALL statement by making a
contiguous copy of the elements Q(1:100:11) before the call and then
copying the elements back to Q(1:100:11) after the return.  Because
the allocated object that was the target of Q was deallocated during
execution of SUBR, the elements are copied back to unallocated
storage.

I believe that the implementations of the CALL statement created by
the compilers I tried were intended to be permitted.  Therefore, I
believe that the program is not standard conforming.  I recognize that
there are other ways of implementing the program that do not have the
problem of copying back the elements of the actual argument.

EDITS: