[MPIWG Fortran] "ELEMENTAL" keyword on mpi_f08 comparison operator functions

[Jeff Hammond]

It should be correct to add ELEMENTAL here and we should encourage that.

I would argue that we should require ELEMENTAL in the place where it says:

   - Overload the operators .EQ. and .NE. to allow the comparison of these
   MPI handles with .EQ., .NE., == and /=.

https://www.mpi-forum.org/docs/mpi-3.1/mpi31-report/node409.htm (I assume
the text is unchanged in MPI-4)

Jeff

On Tue, Mar 8, 2022 at 1:19 AM Jeff Squyres (jsquyres) via mpiwg-fortran <
mpiwg-fortran at lists.mpi-forum.org> wrote:

> Forum Fortran WG --
>
> Any comments?
>
> I got one off-list reply explaining the use of ELEMENTAL, but I'm curious
> as to what the Forum's response should be.
>
> I ask because the use of ELEMENTAL has an impact on MPI application
> portability.  E.g., if the Open MPI family of implementations use ELEMENTAL
> but the MPICH family of implementations do not, that could be confusing for
> users.
>
> --
> Jeff Squyres
> jsquyres at cisco.com
>
> ________________________________________
> From: mpiwg-fortran <mpiwg-fortran-bounces at lists.mpi-forum.org> on behalf
> of Jeff Squyres (jsquyres) via mpiwg-fortran <
> mpiwg-fortran at lists.mpi-forum.org>
> Sent: Tuesday, March 1, 2022 10:24 AM
> To: MPI Forum
> Cc: Jeff Squyres (jsquyres)
> Subject: [MPIWG Fortran] "ELEMENTAL" keyword on mpi_f08 comparison
> operator functions
>
> An Open MPI user this morning requested that we add the "ELEMENTAL"
> keyword to the mpi_f08 module eq / neq operator functions:
> https://github.com/open-mpi/ompi/issues/10057
>
> The only statement I can find in MPI-4.0 about the eq / neq operators is
> section 19.1.2, "Fortran Support Through the mpi_f08 Module", only says the
> following about the operator functions (p793, 22:23):
>
> > Overload the operators .EQ. and .NE. to allow the comparison of these
> MPI handles with .EQ., .NE., == and /=.
>
> This doesn't seem to allow or disallow the use of ELEMENTAL.
>
> What are the pros / cons of adding ELEMENTAL to the eq / neq operator
> functions?
>
> --
> Jeff Squyres
> jsquyres at cisco.com
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-- 
Jeff Hammond
jeff.science at gmail.com
http://jeffhammond.github.io/
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