13.1.1 Aspect Specifications

Certain representation or operational aspects of an entity may be specified as part of its declaration using an aspect_specification, rather than using a separate representation or operational item. The declaration with the aspect_specification is termed the associated declaration. 

An aspect_mark identifies an aspect of the entity defined by the associated declaration (the associated entity); the aspect denotes an object, a value, an expression, a subprogram, or some other kind of entity. If the aspect_mark identifies: 

The usage names in an aspect_definition are not resolved at the point of the associated declaration, but rather are resolved at the end of the immediately enclosing declaration list.

If the associated declaration is for a subprogram or entry, the names of the formal parameters are directly visible within the aspect_definition, as are certain attributes, as specified elsewhere in this International Standard for the identified aspect. If the associated declaration is a type_declaration, within the aspect_definition the names of any components are directly visible, and the name of the first subtype denotes the current instance of the type (see 8.6). If the associated declaration is a subtype_declaration, within the aspect_definition the name of the new subtype denotes the current instance of the subtype.

If the first freezing point of the associated entity comes before the end of the immediately enclosing declaration list, then each usage name in the aspect_definition shall resolve to the same entity at the first freezing point as it does at the end of the immediately enclosing declaration list.

At most one occurrence of each aspect_mark is allowed within a single aspect_specification. The aspect identified by the aspect_mark shall be an aspect that can be specified for the associated entity (or view of the entity defined by the associated declaration).

The aspect_definition associated with a given aspect_mark may be omitted only when the aspect_mark identifies an aspect of a boolean type, in which case it is equivalent to the aspect_definition being specified as True.

If the aspect_mark includes 'Class, then the associated entity shall be a tagged type or a primitive subprogram of a tagged type.

There are no language-defined aspects that may be specified on a renaming_declaration, a generic_formal_parameter_declaration, a subunit, a package_body, a task_body, a protected_body, or a body_stub other than a subprogram_body_stub.

A language-defined aspect shall not be specified in an aspect_specification given on a completion of a subprogram or generic subprogram.

  If an aspect of a derived type is inherited from an ancestor type and has the boolean value True, the inherited value shall not be overridden to have the value False for the derived type, unless otherwise specified in this International Standard.

  Certain type-related aspects are defined to be nonoverridable; all such aspects are specified using an aspect_definition that is a name.

  If a nonoverridable aspect is directly specified for a type T, then any explicit specification of that aspect for any other descendant of T shall be confirming; that is, the specified name shall match the inherited aspect, meaning that the specified name shall denote the same declarations as would the inherited name.

  If a full type has a partial view, and a given nonoverridable aspect is allowed for both the full view and the partial view, then the given aspect for the partial view and the full view shall be the same: the aspect shall be directly specified only on the partial view; if the full type inherits the aspect, then a matching definition shall be specified (directly or by inheritance) for the partial view.

  In addition to the places where Legality Rules normally apply (see 12.3), these rules about nonoverridable aspects also apply in the private part of an instance of a generic unit.

  The Default_Iterator, Iterator_Element, Implicit_Dereference, Constant_Indexing, and Variable_Indexing aspects are nonoverridable.

Depending on which aspect is identified by the aspect_mark, an aspect_definition specifies: 

The identified aspect of the associated entity, or in some cases, the view of the entity defined by the declaration, is as specified by the aspect_definition (or by the default of True when boolean). Whether an aspect_specification applies to an entity or only to the particular view of the entity defined by the declaration is determined by the aspect_mark and the kind of entity. The following aspects are view specific:

All other aspect_specifications are associated with the entity, and apply to all views of the entity, unless otherwise specified in this International Standard.

If the aspect_mark includes 'Class (a class-wide aspect), then, unless specified otherwise for a particular class-wide aspect:

All specifiable operational and representation attributes may be specified with an aspect_specification instead of an attribute_definition_clause (see 13.3).

Any aspect specified by a representation pragma or library unit pragma that has a local_name as its single argument may be specified by an aspect_specification, with the entity being the local_name. The aspect_definition is expected to be of type Boolean. The expression shall be static. Notwithstanding what this International Standard says elsewhere, the expression of an aspect that can be specified by a library unit pragma is resolved and evaluated at the point where it occurs in the aspect_specification, rather than the first freezing point of the associated package.

In addition, other operational and representation aspects not associated with specifiable attributes or representation pragmas may be specified, as specified elsewhere in this International Standard.

If a Legality Rule or Static Semantics rule only applies when a particular aspect has been specified, the aspect is considered to have been specified only when the aspect_specification or attribute_definition_clause is visible (see 8.3) at the point of the application of the rule.

Alternative legality and semantics rules may apply for particular aspects, as specified elsewhere in this International Standard.

At the freezing point of the associated entity, the aspect_specification is elaborated. The elaboration of the aspect_specification includes the evaluation of the name or expression, if any, unless the aspect itself is an expression. If the corresponding aspect represents an expression (as in a precondition), the elaboration has no effect; the expression is evaluated later at points within the execution as specified elsewhere in this International Standard for the particular aspect. 

Implementations may support implementation-defined aspects. The aspect_specification for an implementation-defined aspect may use an implementation-defined syntax for the aspect_definition, and may follow implementation-defined legality and semantics rules.