[mpi-21] Ballot 4 proposal: MPI::COMM_WORLD and MPI::COMM_SELF should be const

[Jeff Squyres]

This is not already on Bill's errata page.

Proposal: Make MPI::COMM_WORLD and MPI::COMM_SELF be "const".

Change MPI-2:B.2 p345:18 from

   // Type: MPI::Intracomm
to
   // Type: const MPI::Intracomm

Rationale: The COMM_WORLD and COMM_SELF C++ handles were erroneously  
not marked "const" because of the incorrect INOUT MPI handle parameter  
designation of the MPI_COMM_SET_ERRHANDLER, MPI_COMM_SET_ATTR, and  
MPI_COMM_SET_ERRHANDLER functions.  This caused the C++ bindings  
methods to not be const, resulting in compile errors if COMM_WORLD was  
const and you invoked any of the methods listed above (e.g.,  
MPI::COMM_WORLD.Set_errhandler(...)).

The proper solution is to have all the MPI handle arguments be IN  
instead of INOUT (covered in another proposal) and therefore have the  
Set_* functions be const (also covered that other proposal).  Once  
that solution is in place, COMM_WORLD and COMM_SELF should be marked  
as "const".  Not that many other predefined MPI C++ handles are  
already const; some erroneously had their "const" designation removed  
in ballot 2 -- a different proposal seeks to restore their "const"  
status.

NOTE: This proposal depends on the "change some INOUT parameters to  
IN" proposal.


-- 
Jeff Squyres
Cisco Systems