To: J3                                                        08-158
From: Bill Long and John Reid
Subject: Allocatable coarrays with intent(out)
Date: 2008 April 25
References: J3/08-007r2 (WG5/N1723)


Discussion:

Jim Xia has pointed out a problem with an intent(out) dummy argument
that is an allocatable coarray or has an allocatable coarray
component.  6.6.3.2, para. 6 makes it clear that such a coarray is
deallocated when the procedure is invoked. This means that there is an
implicit synchronization of all images, but text of the rest of the
draft standard does not allow for this possibility.

We propose that intent(out) be disallowed for such dummy arguments and
provide edits. The option of specifying intent(inout), or no intent,
is a simple alternative for the user. Indeed, this is already
suggested in Note 5.16 for cases where intent(out) is not allowed.

An alternative would be to specify that these deallocations do not
occur for coarrays, but this is irregular.

We could add CALL for a subroutine with such an argument to the list
of image control statements in 8.5.1, but this would not allow for
the function case.


Edits to J3/08-007r2 (WG5/N1723):

[95:p2-] At the end of the first paragraph of 5.3.10 INTENT attribute
add:

C541a An entity with the INTENT(OUT) attribute shall not be an allocatable
coarray or have a subobject that is an allocatable coarray.

[95:p4+] Add this sentence to the end of Note 5.13:

"To avoid this deallocation for coarrays, INTENT(OUT) is not allowed
for a dummy argument that is an allocatable coarray or has a subobject
that is an allocatable coarray."