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H.7 Extensions to Global and Global'Class Aspects

1/5
{AI12-0079-3} In addition to the entities specified in 6.1.2, the Global aspect may be specified for a subtype (including a formal subtype), formal package, formal subprogram, and formal object of an anonymous access-to-subprogram type.

Syntax

2/5
{AI12-0079-3} The following additional syntax is provided for specifying Global and Global'Class aspects, to more precisely describe the use of generic formal parameters and dispatching calls within the execution of an operation:
3/5
extended_global_aspect_definition ::= 
    use formal_parameter_designator
  | do dispatching_operation_specifier
4/5
extended_global_aspect_element ::= 
    use formal_parameter_set
  | do dispatching_operation_set
5/5
extended_global_mode ::= 
    overriding basic_global_mode
6/5
formal_parameter_designator ::= 
    formal_group_designator
  | formal_parameter_name
7/5
formal_parameter_set ::= 
    formal_group_designator
  | formal_parameter_name{, formal_parameter_name}
8/5
formal_group_designator ::= null | all
9/5
formal_parameter_name ::= 
    formal_subtype_mark
  | formal_subprogram_name
  | formal_access_to_subprogram_object_name
10/5
dispatching_operation_set ::= 
    dispatching_operation_specifier{, dispatching_operation_specifier}
11/5
dispatching_operation_specifier ::= 
    dispatching_operation_name (object_name)

Name Resolution Rules

12/5
{AI12-0079-3} A formal_parameter_name shall resolve to statically denote a formal subtype, a formal subprogram, or a formal object of an anonymous access-to-subprogram type.
13/5
{AI12-0079-3} The object_name that is associated with an overriding mode shall resolve to statically denote a formal object, or a formal parameter of the associated entity.
14/5
{AI12-0079-3} The object_name of a dispatching_operation_specifier shall resolve to statically name an object (including possibly a formal parameter) of a tagged class-wide type T'Class; the dispatching_operation_name of the dispatching_operation_specifier shall resolve to statically denote a dispatching operation associated with T.

Static Semantics

15/5
{AI12-0079-3} The presence of the reserved word overriding in a global mode indicates that the specification is overriding the mode of a formal parameter with another mode to reflect the overall effect of an invocation of the callable entity on the state associated with the corresponding actual parameter.
16/5
{AI12-0079-3} The extended_global_aspect_definition and extended_global_aspect_element can be used to define as part of the Global aspect the formal parameter set and the dispatching operation set used within an operation. The formal parameter set is identified by a set of formal parameter names after the reserved word use. Alternatively, the reserved word null may be used to indicate none of the generic formal parameters, or all to indicate all of the generic formal parameters, of any enclosing generic unit (or visible formal package) might be used within the execution of the operation. If there is no formal parameter set specified for an operation declared within a generic unit, it defaults to use all.
17/5
{AI12-0079-3} The dispatching operation set is identified by a set of dispatching_operation_specifiers after the reserved word do. It indicates that the Global effects of dispatching calls that match one of the specifiers need not be accounted for by other elements of the Global aspect, but are instead to be accounted for by the invoker of the operation. A dispatching call matches a dispatching_operation_specifier if the name or prefix of the call statically denotes the same operation(s) as that of the dispatching_operation_specifier, and at least one of the objects controlling the call is denoted by a name that statically names the same object as that denoted by the object_name of the dispatching_operation_specifier. In the absence of any dispatching_operation_specifiers, all dispatching calls within the operation are presumed to have the effects determined by the set of Global'Class aspects that apply to the invoked dispatching operation.
17.a/5
Ramification: The object “controlling the call” is not necessarily a controlling parameter of the call if the call is a function with a controlling result or has parameters that is such a function. It is one of the objects that provide the dispatching tag used for the call; that could, for example, be a parameter of a function used as a parameter to the call, or an object being assigned to, or a parameter of an enclosing call. 
18/5
{AI12-0079-3} The Global aspect for a subtype identifies the global variables that might be referenced during default initialization, adjustment as part of assignment, finalization of an object of the subtype, or conversion to the subtype, including the evaluation of any assertion expressions that apply. If not specified for the first subtype of a derived type, the aspect defaults to that of the ancestor subtype; if not specified for a nonderived first subtype the aspect defaults to that of the enclosing library unit. If not specified for a nonfirst subtype S, the Global aspect defaults to that of the subtype identified in the subtype_indication defining S.
19/5
{AI12-0079-3} The Global'Class aspect may be specified for the first subtype of a tagged type T, indicating an upper bound on the Global aspect of any descendant of T. If not specified, it defaults to Unspecified.

Legality Rules

20/5
{AI12-0079-3} For a tagged subtype T, each mode of its Global aspect shall identify a subset of the variables identified by the corresponding mode, or by the in out mode, of the Global'Class aspect of the first subtype of any ancestor of T.
21/5
{AI12-0079-3} If the formal parameter set is anything but all in the Global aspect for an operation declared within a generic unit, then the only generic formal subtypes that may be used, the only formal subprograms that may be called, and the only formal objects of an anonymous access-to-subprogram type that may be dereferenced as part of a call or passed as the actual for an access parameter, are those included in the formal parameter set.
22/5
{AI12-0079-3} Any dispatching call occurring within the operation that does not match a dispatching_operation_specifier is checked using the Global'Class aspect(s) applicable to the dispatching operation; if there is a match, there is no checking against other elements of the Global aspect(s) applicable at the point of call.

Extensions to Ada 2012

22.a/5
{AI12-0079-3} These extensions to the Global aspect are new. 

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