Yes, that's the way the original C++ bindings were implemented. But it's not required or necessary to do that; that C errhandler could easily be cached somewhere else. More specifically, isn't it better to have a const object to allow for compiler optimizations? (I'm not a compiler guru, but I thought the point of why we originally made the C++ handles be const was on the argument for potential compiler optimizations) On Jan 18, 2008, at 8:35 PM, Erez Haba wrote:
For example an implementation might choose to cache the error handler for MPI::COMM_WORD (in the MPI::Comm object) and call it itself on error so it can pass in the right object to the error handler. Thus requiring MPI::COMM_WORLD not to be const.
-----Original Message----- From: owner-mpi-21_at_[hidden] [mailto:owner-mpi-21_at_[hidden]] On Behalf Of Jeff Squyres Sent: Friday, January 18, 2008 11:14 AM To: mpi-21_at_[hidden] Cc: mpi-21_at_[hidden] Subject: [mpi-21] const C++ MPI handles (take 2)
On Jan 18, 2008, at 2:02 PM, Erez Haba wrote:
Okay; about one issue at a time.
Changing mail subject to reflect the discussion...
*For this sentence* it does not matter what's a common usage for C++ global variables. Some MPI implementations would need to have non- const qualified global objects.
Why? As I understand it, most (all?) MPI C++ implementations currently only require some objects to be non-const because of the standard-related issue that was already raised (Set_attr(), Set_name(), Set_errhandler() methods not having const variants). Is there a reason that an implementation would *need* MPI handles to be non-const?
Per my prior mail, I believe that the standard should specify that some of the methods on these classes should have const and non-const variants, and then it should be fine to require that the predefined handles be const.
So the question is still open: what's common practice in the C++ community regarding const/non-const global variable specification? This question will be moot if you can demonstrate that an implementation would need non-const C++ MPI predefined handles.
-- Jeff Squyres Cisco Systems
-- Jeff Squyres Cisco Systems