10-152
To: J3
From: Robert Corbett
Subject: Interpretation Request: optional arguments and ASSOCIATED
Date: 2010 May 31

All references are to J3/10-007.

QUESTION:

If the actual argument associated with the dummy argument TARGET
of the intrinsic function ASSOCIATED is a disassociated pointer,
is the dummy argument TARGET to be treated as an optional
argument that is not present or as an argument that is present?

ANSWER:

The dummy argument TARGET should be treated as an argument that
is present.

DISCUSSION:

This problem was created by the Fortran 2008 extension that
declares that a dummy argument is not present if it corresponds
to an actual argument that is a disassociated pointer
[12.5.2.12p1, 299:15-17].

Among the solutions that have been suggested are

     (1) removing the extension,

     (2) restricting the extension to apply only to user-defined
	 functions,

     (3) adding an exception to the extension for the intrinsic
         function ASSOCIATED,

     (4) changing the specification of ASSOCIATED in
         [17.7.16, 330:7-42] to specify two signatures.

As attractive as the first two solutions are, I initially
favored solution (3) as it caused the least change to the
language as defined in recent drafts.  I proposed to add text
to Section 12.5.2.12 specifying the exception.  Over time, I
changed my mind; I now favor solution (4).

I initially favored solution (3) over solution (4) because
solution (4) does not treat the dummy argument TARGET as not
present when the corresponding actual argument is an optional
argument that is not present.  That functionality is in
Fortran 2003, and I did not think it should be removed.  The
more I thought about the issue, the more I was convinced that
that functionality is useless except for programs written for
test suites.  I am now convinced that removing that
functionality improves the language by making it possible for
a processor to treat use of that functionality as the error
it almost certainly is.

EDITS:

[13.7.16, 330:7]
Replace "ASSOCIATED (POINTER [,TARGET])" with
"ASSOCIATED (POINTER) or ASSOCIATED(POINTER, TARGET)".

[13.7.16, 330:18]
Replace "is absence" with "does not appear".

[13.7.16, 330:19]
Replace "is present" with "appears".

[13.7.16, 330:23]
Replace "is present" with "appears".

[13.7.16, 330:26]
Replace "is present" with "appears".

[13.7.16, 330:30]
Replace "is present" with "appears".

[13.7.16, 330:33]
Replace "is present" with "appears".