! NOTE: This class implements the Singleton pattern - there should
! be only one GridManager for the application. However,
! testing requires multiple instances. To reflect this
! intent this file contains 2 modules. The first one
! “MAPL_GridManager_private” makes the derived type public,
! and is useful for testing. The 2nd module
! “MAPL_GridManagerMod” is intended for general use, and
! does not export the derived type.