J3/14-137r1
To: J3
Subject: C1296 (constraint on pure subprograms)
From: Van Snyder
Date: 2014 May 29

1. Introduction
===============

C1296 [14-007r1:314:28-315:2] says

"In a pure subprogram any designator with a base object that is in
 common or accessed by host or use association, is a dummy argument of a
 pure function, is a dummy argument with the INTENT (IN) attribute, is a
 coindexed object, or an object that is storage associated with any such
 variable, shall not be used

 (1) in a variable definition context (16.6.7),
 (2) as the <data-target> in a <pointer-assignment-stmt>,
 (3) as the <expr> corresponding to a component with the POINTER
     attribute in a <structure-constructor>,
 (4) as the <expr> of an intrinsic assignment statement in which the
     variable is of a derived type if the derived type has a pointer
     component at any level of component selection,
 (5) as the <source-expr> in a SOURCE= clause if the designator is of a
     derived type that has an ultimate pointer component, or
 (6) as an actual argument corresponding to a dummy argument with INTENT
     (OUT) or INTENT (INOUT) or with the POINTER attribute.

C1282 requires a dummy argument of a pure function to have the
INTENT(IN) or VALUE attribute.

C1296 fortunately does not constrain local variables of pure
subprograms.  Dummy arguments with the VALUE attribute are effectively
local variables.

Therefore, for a dummy argument of a pure function that has the VALUE
attribute, there is no problem that is solved by C1296.

Therefore, it is enough for C1296 to have "is a dummy argument with the
INTENT(IN) attribute".  It doesn't need "is a dummy argument of a pure
function".

Most of the prohibition in item (6) against appearing as an actual
argument corresponding to a dummy argument with the INTENT(OUT) or
INTENT(INOUT) attribute duplicates 16.6.7p1(12), which is cited in item
(1).

2. Edits to 14-007r1
====================

[xviii:Somewhere in the intro concerning extensions]

" o A dummy argument of a pure procedure may appear in variable
    definition and similar contexts if it has the VALUE attribute and
    does not have the INTENT(IN) attribute."

[314:29] Delete ", is a dummy argument of a pure function"

[314:30] Insert "is" before "an" (for consistency with the rest of the
sentence).

[314:37] Replace "clause" with "specifier".

[315:1-2] Delete "with INTENT(OUT) or INTENT(INOUT) or" because it
duplicates 16.6.7p1(12).