[Mpi-forum] Reserved MPI_ prefix & namespace in C and Fortran

[N.M. Maclaren]

On Aug 24 2012, William Gropp wrote:
>
> The intent of the Forum has always been that all names that begin with 
> MPI_ or PMPI_, and the MPI namespace, are reserved for MPI. The mistake 
> (a common one) was to attempt to enumerate all of the items to which this 
> applies. Rather than attempt to cover everything, I would prefer changing 
> the text to match the indent; it can mention specific categories as 
> examples but should not attempt to list them, as this is always error 
> prone.

While I think that is correct, I am afraid that the wording isn't, for
any of the languages.

If C++ is deleted, then the reference to namespaces should be, too;
while C has such a concept, it's wildly different, and you don't want
to go there :-)  If it isn't, it should be explicitly the namespaces
MPI and PMPI, as at present.

>> The solution is very simple, an MPI-2 errata ticket changing
>> MPI-2.2, lines 15-16 into (addition marked with {...}):
>> 
>>   "Programs must not declare variables, functions, 
>>    { constants, macros, types, or namespaces }
>>    with names beginning with the prefix MPI_."

The killer is that is both too restrictive and too lax - you also have
labels, tags and members (C99 6.2.3), and local names are a problem
onbly together with the header.

>> And for Fortran on p17:41-42 (addition marked with {...}):
>> 
>>   "Programs must not declare variables, parameters, functions, 
>>    { derived types, or abstract interfaces }
>>    with names beginning with the prefix MPI_. 

The same applies, in very different ways.  Fortran has a vast number
of other classes of name, but declaring local ones will cause trouble
only in combination with the header.

Better wording might be, for C:

    Other than by including the header "mpi.h", programs shall not
    declare entities with external names beginning with the prefix
    MPI_.  In a translation unit that includes the header "mpi.h",
    programs shall not declare any other entities with names
    beginning with the prefix MPI_.

And for Fortran:

    Other than by using one of the modules "mpi_f08" or "mpi" or
    including the header "mpif.h", programs shall not declare
    entities with external names beginning with the prefix MPI_.
    In a program unit that uses one of the modules "mpi_f08" or "mpi"
    or includes the header "mpif.h", programs shall not declare any
    other entities with names beginning with the prefix MPI_.


Regards,
Nick Maclaren.