The GNAT implementation of remote access-to-classwide types is organized as described in AARM section E.4 (20.t): a value of an RACW type (designating a remote object) is represented as a normal access value, pointing to a "stub" object which in turn contains the necessary information to contact the designated remote object. A call on any dispatching operation of such a stub object does the remote call, if necessary, using the information in the stub object to locate the target partition, etc.
For a prefix T that denotes a remote access-to-classwide type,
T'Stub_Type denotes the type of the corresponding stub objects.
By construction, the layout of T'Stub_Type is identical to that of
type RACW_Stub_Type declared in the internal implementation-defined
unit System.Partition_Interface. Use of this attribute will create
an implicit dependency on this unit.