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.]

Language Design Principles

1.a

The restrictions governing a remote types package are similar to those for a declared pure package. However, the restrictions are relaxed deliberately to allow such a package to contain declarations that violate the stateless property of pure packages, though it is presumed that any state-dependent properties are essentially invisible outside the package.

Syntax

{categorization pragma (Remote_Types) [partial]} {pragma, categorization (Remote_Types) [partial]} The form of a pragma Remote_Types is as follows:

pragma Remote_Types[(library_unit_name)];

Legality Rules

{remote types library unit} 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;

7.a

Reason: This is essentially a ``methodological'' restriction. A separate copy of a remote types package is included in each partition that references it, just like a normal package. Nevertheless, a remote types package is thought of as an ``essentially pure'' package for defining types to be used for interpartition communication, and it could be misleading to declare visible objects when no remote data access is actually being provided.

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.

8.a

Reason: This is to prevent the use of the predefined Read and Write attributes of an access type as part of the Read and Write attributes of a visible type.

9/1

{8652/0082} {remote access type} An access type declared in the visible part of a remote types or remote call interface library unit is called a remote access type. {remote access-to-subprogram type} {remote access-to-class-wide type} Such a type shall be: ~~either an access-to-subprogram type or a general access type that designates a class-wide limited private type.~~

9.1/1

{8652/0082} an access-to-subprogram type, or

9.2/1

{8652/0082} 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.

9.3/1

{8652/0081} 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:

14/1

{8652/0083} 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~~the types of all the non-controlling formal parameters shall have~~ 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;

16/1

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'').;

17/1

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.;

17.a

Reason: All three of these restrictions are because there is no storage pool associated with a remote access-to-class-wide type.

NOTES

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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