E.2.2 Remote Types Library Units
A remote types library unit supports the definition of types intended for use in communication between active partitions.
The form of a pragma Remote_Types is as follows:
A remote types library unit is a library unit to which the pragma Remote_Types applies. The following restrictions apply to the declaration of such a library unit:
- it shall be preelaborable;
- it shall depend semantically only on declared pure, shared passive, or other remote types library units;
- it shall not contain the declaration of any variable within the visible part of the library unit;
- if the full view of a type declared in the visible part of the library unit has a part that is of a non-remote access type, then that access type, or the type of some part that includes the access type subcomponent, shall have user-specified Read and Write attributes.
An access type declared in the visible part of a remote types or remote call interface library unit is called a remote access type. Such a type shall be:
- an access-to-subprogram type, or
- a general access type that designates a class-wide limited private type or a class-wide private type extension all of whose ancestors are either private type extensions or limited private types.
A type that is derived from a remote access type is also a remote access type.
The following restrictions apply to the use of a remote access-to-subprogram type:
- A value of a remote access-to-subprogram type shall be converted only to another (subtype-conformant) remote access-to-subprogram type;
- The prefix of an Access attribute_reference that yields a value of a remote access-to-subprogram type shall statically denote a (subtype-conformant) remote subprogram.
The following restrictions apply to the use of a remote access-to-class-wide type:
- The primitive subprograms of the corresponding specific limited private type shall only have access parameters if they are controlling formal parameters; each non-controlling formal parameter shall have either a nonlimited type or a type with Read and Write attributes specified via an attribute_definition_clause;
- A value of a remote access-to-class-wide type shall be explicitly converted only to another remote access-to-class-wide type;
- A value of a remote access-to-class-wide type shall be dereferenced (or implicitly converted to an anonymous access type) only as part of a dispatching call where the value designates a controlling operand of the call (see E.4, Remote Subprogram Calls).
- The Storage_Pool and Storage_Size attributes are not defined for remote access-to-class-wide types; the expected type for an allocator shall not be a remote access-to-class-wide type; a remote access-to-class-wide type shall not be an actual parameter for a generic formal access type.
5 A remote types library unit need not be pure, and the types it defines may include levels of indirection implemented by using access types. User-specified Read and Write attributes (see 13.13.2) provide for sending values of such a type between active partitions, with Write marshalling the representation, and Read unmarshalling any levels of indirection.
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Copyright © 2000 The MITRE Corporation, Inc. Ada Reference Manual