07-186

To:          J3
From:        Van Snyder
Subject:     Automatic polymorphic variables
Date: 2007 April 23



1 Introduction

In Fortran 2003 we left polymorphic assignment to Fortran 2008. We were
fortunately able to develop a compatible extension. Automatic variables
can automatically get values for length parameters or array bounds, but
cannot get their type. Variables of the same type as the dynamic type of a
dummy argument or a module variable would be useful. There is no obvious
extension that is compatible with MOLD=, so if we anticipate doing this,
now is the time to do it (assuming we don't want a kludge). As things
stand, the only way to get them is to allocate them. Automatic variables
are simpler to program, and might have a slight edge of performance over
explicitly allocated ones because the processor might invoke the memory
manager only once when the specifcation part is elaborated to allocate
space for all local variables, automatic or otherwise.

2 Proposal

Allow TYPEOF(variable ) in place of declaration-type-spec except in
IMPLICIT, or in place of type-spec in an array constructor or ALLOCATE
statement. Delete MOLD= from the ALLOCATE statement.

3 Edits

Edits refer to07-007r1. Page and line numbers are displayed in the margin.
Absent other instructions, a page and line number or line number range
implies all of the indicated text is to be replaced by associated text,
while a page and line number followed by + (-) indicates that associated
text is to be inserted after (before) the indicated line. Remarks are
noted in the margin, or appear between [ and ] in the text.

[47:22+] ----------------------------------------------------------------
                                    or TYPEOF ( <variable> )

[47:28+] ----------------------------------------------------------------
                                    or TYPEOF ( <variable> )

[47:37] ------------------------------------------------------------------
[Editor: Append a sentence to the paragraph:]

If TYPEOF(<variable>) appears the declared and dynamic types and type
parameters specified are those of <variable>.

[65:7+]------------------------------------------------------------------
C440a (R441) If <declaration-type-spec> is TYPEOF(<variable>), <variable>
        shall not be polymor- phic and its type parameter values shall be
        specified by initialization expressions.

[84:14] ------------------------------------------------------------------
[Editor: Insert "If <type-spec> appears and is TYPEOF(<variable>) the
array constructor is polymor- phic if and only if <variable> is
polymorphic. Every type parameter of <variable> shall have a defined
value." before "If ". Insert "and is not TYPEOF(<variable>)" after
"appears".]

[84:15-16] ---------------------------------------------------------------
[Editor: Replace "this type and type parameters" by "the type and type
parameters of the <array- constructor>".]

[87:15-16] ---------------------------------------------------------------
[Editor: Insert "If TYPEOF(<variable>) appears the entities are
polymorphic if and only if <variable> is polymorphic. Every type parameter
of <variable> shall have a defined value. If TYPEOF does not appear, the".
before second "The"]

[88:8+]------------------------------------------------------------------
C503a (R503) If <declaration-type-spec> is TYPEOF(<variable>) and
       <variable> is polymorphic, <object-name> shall not be the name of
       a dummy argument or function result variable.

[88:36] ------------------------------------------------------------------
[Editor: Insert ", or if <declaration-type-spec> is TYPEOF(<variable>) and
<variable> is polymorphic or has a type parameter that is assumed,
deferred, or specified by a specification expression" at the end of the
sentence.]

[88:37+] ----------------------------------------------------------------
C513a An automatic data ob ject shall not have the ALLOCATABLE, EXTERNAL,
      INTRINSIC, PARAMETER, POINTER or SAVE attribute.

[110:7+] ----------------------------------------------------------------
C579a (R560) The <declaration-type-spec> shall not be TYPEOF(<variable>).

[127:13] -----------------------------------------------------------------
[Editor: Delete.]

[130:15] -----------------------------------------------------------------
If <type-spec> appears and consists of TYPEOF(<variable>), the value of
<variable> need not be defined, but the values of its type parameters
shall be defined.

[306:19+] ---------------------------------------------------------------
C1215a (R1212) If <declaration-type-spec> is TYPEOF(<variable>),
        <variable> shall not be poly- morphic.

[326:30+] ---------------------------------------------------------------
C1248a (R1226) If <declaration-type-spec> is TYPEOF(<variable>),
        <variable> shall not be polymorphic.