[MPI3 Fortran] Results of recent J3 Fortran meeting

[N.M. Maclaren]

On Oct 21 2010, Bill Long wrote:
>> 
>> Except for the last sentence, that is true.  But one of MPI's major
>> requirements is that it should be able to handle Fortran default types,
>> and NOT force every program to use the C-interoperability KINDs to
>> call MPI!  Sorry, but there IS an issue.
>> 
>
>OK, I agree that there is a general issue for MPI with non-interoperable 
>types.  We have a type code for that - CFI_type_unspecified.   I assume 
>that, if the MPI routines are expecting data objects of Fortran types 
>that have no corresponding C types (and hence there is little that can 
>be done with them in C other than memory copies) then the actual intent 
>is to only make memory copies.  In that case, knowing the size of a 
>single character is unimportant. All you need is the base_addr, 
>elem_len, rank, and dim[] information.

That is true, but why do you assume that they have no corresponding C
types?  C90 had a fixed number of integer types, but C99 has an arbitrary
number.  It is also possible to translate between any number of bytes
and an integer/character in C - all you need to know is how many there
are.

What I said at the beginning, and which was my point, is that this approach
is the least FUTURE-PROOF of the approaches, not that it was incompatible
with the existing interoperability design.  And one of the things that I
hope Fortran has learnt is that assuming that requirements aren't going to
become important is a mistake.  It isn't possible to design for everything,
but maximising the flexibility is definitely good.

Regards,
Nick Maclaren.