J3/02-161

To:      J3
From:    Dan Nagle
Subject: Remove some restrictions on Optional Dummy Arguments
Date:    9 Mar 02

During the discussion at 160 re arguments to IEEE module
intrinsics, some unhelpful restrictions on non-present procedure
arguments were encountered.  Current constraints encourage
the use of local variables in place of optional arguments, since
the non-present argument can only appear as the argument
of the present() intrinsic.

Specifically, the following "natural" constructions are at present
illegal:

real( kind= myreal), optional :: foo   ! note that foo's kind is known
real( kind= kind( foo)) :: local_foo   ! but foo might not be present
...
opt_arg: if( present( foo) )then         ! the only legal usage here
   local_foo = foo
else opt_arg
   local_foo = 42.0_kind( foo)   ! or huge( foo) etc.
endif opt_arg
...                                  ! use local_foo for the rest of the
procedure

Since the inquiry intrinsics do not query the value of their
arguments, but only such compile time quantities as kind,
and since there are reasonable uses of such information,
a slight relaxation of the rules for non-present dummys
is proposed.

Specifically, the use of non-present dummys in compile time
intrinsics should be allowed.  I think this list is reasonably limited to:
kind(), those listed in 13.5.6 Numeric Inquiry Functions, bit_size().
(I'll happily modify this list to meet J3's concerns.)

Edits:

(Edits are against 02-007, I'll update them to the r1 if
this doesn't go down in flames before then :-)

(Modify restrictions listed in 12.4.1.6)

258:15 Replace "PRESENT" with
"PRESENT, KIND, BIT_SIZE or one of the Numeric Inquiry Functions
(13.5.6)"