Pure virtual MPIComm() method in Comm

[tom-j-h]

Is your feature request related to a problem? Please describe.

The Atlas function atlas::mpi::comm() returns a Comm. From this, I need to get the internal MPI_Comm, to pass to the netCDF C API functions. Parallel (derived from Comm) has the method MPIComm() which will give me this, but since I've only got a Comm, I'd have to use a dynamic_cast to access this.

Describe the solution you'd like

It would be nice if MPIComm() was a pure virtual function of Comm, and it's implementation in Serial could perhaps throw an exception or return MPI_COMM_SELF (not sure what would be best here...).

Describe alternatives you've considered

dynamic_cast, as explained.

Additional context

Related to same work described in ecmwf/atlas#260 !

Organisation

Met Office

[tom-j-h]

On reflection I'm happy with the dynamic cast here