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Date: Sat, 29 Nov 2008 21:34:04 +0100
From: bader-reinhold@t-online.de (Reinhold Bader)
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Cc: WG5 <sc22wg5@open-std.org>,
	Rolf Rabenseifner <rabenseifner@hlrs.de>
Subject: Comment on N1761
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Hello,

The TR 29113 draft contains the following example code:

interface MPI_send
   subroutine MPI_send_old (buffer, n) bind(c,name="MPI_send")
      type(*), dimension(*) :: buffer ! Passed by simple address
      integer(c_int),value :: n
   end subroutine
   subroutine MPI_send_new (buffer) bind(c,name="MPI_send_new")
      type(*), dimension(..), contiguous :: buffer
         ! Passed by descriptor including the shape and type
   end subroutine
end interface

real :: x(100), y(10,10)

! These will invoke MPI_send_old
call MPI_send(x,size(x)) ! Passed by address
call MPI_send(y,size(y)) ! Sequence association                  <----non-conforming?
call MPI_send(y(:,1),size(y,dim=1)) ! Pass first column of y
call MPI_send(y(1,5),size(y,dim=1)) ! Pass fifth column of y

! These will invoke MPI_send_new
call MPI_send(x) ! Pass a rank-1 descriptor
call MPI_send(y) ! Pass a rank-0 descriptor                     <---Typo? ("rank-2")
call MPI_send(y(:,1)) ! Passed by descriptor without copy
call MPI_send(y(1,5)) ! Illegal: No sequence association


In my opinion, the marked line would be non-conforming even under the
additional rules specified by TR29113, since it contravenes p290, para 13
of the F2008 draft standard 08-007r2, which disallows matching of actual
arguments of arbitrary ranks to the assumed size dummy of rank one *for
a generic interface*.

If my critique is correct, there are the following choices:

* Give up having a generic interface, or use the assumed size only
  for 1-d arrays. This would only require correcting the above example.
* Add an exception to the above-mentioned rule, applying for TYPE(*) arguments
  of assumed size. One possibility would be to allow a match with the specific
  with the largest rank smaller or equal to the actual arguments'; this might be
  reasonable not only for TYPE(*), but is probably not feasible due to
  backward incompatibility.

I'm also pointing out a typo in the use of the assumed rank part.

Best Regards

-- 
 Dr. Reinhold Bader

 Leibniz-Rechenzentrum, Abt. Hochleistungssysteme | Tel. +49 89 35831 8825
 Boltzmannstr. 1, 85748 Garching                  | Fax  +49 89 35831 9700