Comment (by Roland Haas):

Note that to find out the total number of patches (maps) one still has to call the aliased functon GetMaps. Not sure if there is a legit use for that information though (there is also not official way to find out the total number of components [not MPI ranks]). Also note that the assumption cctk_patch == 0 → Cartesian patch is most likely not true for eg the 6 patch cubed sphere system (which has no Cartesian block in the center). The function to query this would be MultiPatch_MapIsCartesian in the Coordinates thorn (which only requires knowledge of cctk_patch and of course calls it map).

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2586/new-cgh-field-cctk_patch