J3/13-211

To: J3
From: Van Snyder
Subject: Reduce restrictions on VALUE
Date: 2013 December 19

Title: Reduce restrictions on VALUE

Submitted by: Van Snyder

Status: For consideration

Basic functionality: Allow a dummy argument with the VALUE attribute to
have the POINTER, ALLOCTABLE, VOLATILE, or OPTIONAL attribute, the
latter only if it is not a dummy argument of a BIND(C) subprogram, is
not an assumed-shape or assumed-size array, and has no assumed length
parameters.

Rationale: Reduces the number of statements and temporary variables, and
thereby long-term cost.

Estimated impact: Minor

Markham M6 conformance: Remove simple deficiencies, discrepancies, and
pointless restrictions.

Detailed specification:

There is no problem for a dummy argument with the VALUE attribute to
have the POINTER attribute: It gets its initial pointer association
status from the corresponding actual argument, if the actual argument is
a pointer, or becomes pointer associated with the actual argument if the
actual argument is not a pointer.

There is no problem for a dummy argument with the VALUE attribute to be
allocatable: If the actual argument is not allocatable the dummy
argument is initially allocated and gets its shape and value from the
corresponding actual argument.  If the actual argument is allocatable,
the dummy argument gets its initial allocation status, and, if
allocated, its value, bounds, and deferred length parameter values, from
the corresponding actual argument.

There is no problem for a dummy argument with the VALUE attribute to be
VOLATILE.  Its volatility commences after it gets its value.

There is no problem for a dummy argument with the VALUE attribute to be
optional (except for BIND(C) procedures), and yet to exist even if the
corresponding actual argument is absent, unless it has assumed shape,
assumed size, or an assumed length parameter.  If it is absent and
neither allocatable nor a pointer its initial value -- except for
default initialized subcomponents -- is undefined (but that doesn't
prevent the procedure from defining it).  If it is absent and
allocatable it is initially not allocated (but that doesn't prevent the
procedure from allocating it).  If it is absent and a pointer its
initial pointer association status is undefined (but that doesn't
prevent the procedure from defining it).

Draft edits: To estimate scope of project

Replace C588 with

C588 An entity with the VALUE attribute shall not have the INTENT(INOUT)
     or INTENT(OUT) attribute.  If it has the OPTIONAL attribute it
     shall not be an assumed-shape or assumed-size array, or have an
     assumed length parameter.

{ Prohibition against simultaneous OPTIONAL and BIND(C) is covered by
  C1255a in TS 29113 (N1917). }

Replace 12.5.2.3p4:

"A nonpointer nonallocatable dummy argument with the VALUE attribute
becomes associated with a definable anonymous data object.  If the
argument is present its initial value is the value of the actual
argument.  Otherwise it is initially undefined, except for default
initialized subcomponents."

In 12.5.2.3p5 insert "without the VALUE attribute" after "dummy
argument".

Insert paragraphs after 12.5.2.3p5:

"A present pointer dummy argument with the VALUE attribute has the same
pointer association status as the corresponding actual argument.  The
initial association status of an absent pointer dummy argument that has
the VALUE attribute is undefined.

"A present allocatable dummy argument with the VALUE attribute has the
same allocation status as the corresponding actual argument.  If the
actual argument is allocated the initial bounds, value, and values of
deferred length parameters of the dummy argument are the same as the
actual argument.  The initial allocation status of an absent allocatable
dummy argument that has the VALUE attribute is deallocated."