To: J3                                                          08-284
From: John Reid, Bill Long
Subject: Interpretation re pure procedures and VOLATILE
Date: 2008 October 30

NUMBER: F03/xxxx
TITLE: References to VOLATILE variables in pure procedures
KEYWORDS: VOLATILE, pure
DEFECT TYPE: Error
STATUS: J3 consideration in progress

QUESTION:
Was it intended to allow a VOLATILE variable to be referenced
in a pure procedure?

ANSWER:
No. For example, it was intended that the result of invoking a pure
function in a FORALL assignment statement should never depend on the
order in which the invocations are executed, see NOTE 12.44.

DISCUSSION:
The arguments of a PURE function are required to have intent(in) so
cannot be VOLATILE (see constraint C526). However, a VOLATILE variable
may be accessed from the host, a module, or a common block.  Also a
non-VOLATILE variable may be accessed and given the VOLATILE
attribute.  The value of a variable with the VOLATILE attribute might
change between invocations of the function in ways incompatible with
the design intended for pure functions.

EDIT:
[286:22+] In 12.6, Pure procedures, add a new constraint:

"C1271a The value, allocation status, or pointer association status of
        a variable with the VOLATILE attribute shall not be referenced
        or defined in a pure subprogram."


SUBMITTED BY: John Reid and Bill Long

HISTORY:
N1745 m186 Problem raised by Nick Maclaren for VOLATILE coarrays.