From: Jeff Squyres <jsquyres@XXXXXXXXX>
Date: January 23, 2008 12:26:55 PM CST
To: mpi-21@XXXXXXXXXXXXX
Subject: Re: [mpi-21] const MPI C++ handles
Reply-To: mpi-21@XXXXXXXXXXXXX

On Jan 23, 2008, at 12:55 PM, Erez Haba wrote:

> What is I implement the C++ binding but I don't have an underlying  
> C implementation? The C++ objects will hold all the relevant  
> information and by defining MPI::COMM_WORLD const, you make it  
> immutable.

You still have to supply handle-like semantics, so you can't put the  
state in the MPI handle (not even MPI::COMM_WORLD).  E.g.:

    MPI::Intracomm a = b;
    b.Set_name("foo");
    a.Get_name(name, sizeof(name));

The string put into the name variable *must* be "foo".  This means  
that you can't store the name on the b handle, but rather on the  
underlying MPI communicator.

You can easily construct nastier examples where the original handle  
would go out of scope (but the underlying MPI communicator must still  
exist), so elaborate reference schemes (where a simply references to  
b) won't work, either.

-- 
Jeff Squyres
Cisco Systems