[MPIWG Fortran] MPI_SIZEOF: Errata required (was: Another MPI_SIZEOF question)

[Bill Long]

On Jun 11, 2014, at 3:18 PM, Jeff Squyres (jsquyres) <jsquyres at cisco.com> wrote:

> On Jun 11, 2014, at 4:07 PM, "Jeff Squyres (jsquyres)" <jsquyres at cisco.com> wrote:
> 
>> I open to suggestions.
>> 
>> 1. One obvious possibility is to re-instate "extended Fortran support"-like language, a la MPI-2.2.  This does not make it possible to have MPI_SIZEOF in mpif.h, however, so I don't think it really solves the problem.
>> 
>> 2. Another possibility is to say that MPI_SIZEOF is only available in the mpi and mpi_f08 modules (e.g., add an exception in MPI-3.x 17.1.4 saying that MPI_SIZEOF support is excluded from mpif.h).  Per Bill Gropp's email (http://lists.mpi-forum.org/mpiwg-fortran/2014/06/1572.php), we'll actually have to add exceptions / remove references to overloading for all mpif.h cases -- not just MPI_SIZEOF.
> 
> 
> I accidentally hit "send" before adding:
> 
> 3. Bill Gropp's suggestion (http://lists.mpi-forum.org/mpiwg-fortran/2014/06/1592.php) of removing "Fortran 77" support entirely.
> 
> I'm not a big fan of effectively removing support for older Fortran compilers in a point release of MPI (i.e., 3.1 -- 4.0 might be a better candidate for this).  But I acknowledge Bill's warning (the "As an alternative..." paragraph is the above-cited email) about selectively editing the text to allow "Fortran 77" compilers.
> 
> Indeed, the problem is more insidious than we initially thought -- because it's not just "Fortran 77" codes that are affected, but any source.f code, because it will likely invoke compiler defaults that will preclude using INTERFACE blocks and other modern Fortran constructs.  


I’m not aware of any compiler like that, but I suppose it is possible.  But, in general this seems like a pointless / silly convention to impose.  A compiler switch to change the source form default is reasonable (and common).  But why would you remove parts of the language?


> 
> Hence, mpif.h really is stuck in the past.  It is possible that the only reasonable solution is to make mpif.h safe for source.f-like behavior, and then deprecate mpif.h in MPI-4.0.
> 

The idea of include files in Fortran of any sort is “stuck in the past”.

Cheers,
Bill



> -- 
> Jeff Squyres
> jsquyres at cisco.com
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Bill Long                                                                       longb at cray.com
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