4.1.4 Attributes

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An attribute is a characteristic of an entity that can be queried via an attribute_reference or a range_attribute_reference.

Syntax

attribute_reference ::= prefix'attribute_designator

attribute_designator ::=
   identifier[(static_expression)]
 | Access | Delta | Digits

range_attribute_reference ::= prefix'range_attribute_designator

range_attribute_designator ::= Range[(static_expression)]

Name Resolution Rules

In an attribute_reference, if the attribute_designator is for an attribute defined for (at least some) objects of an access type, then the prefix is never interpreted as an implicit_dereference; otherwise (and for all range_attribute_references), if the type of the name within the prefix is of an access type, the prefix is interpreted as an implicit_dereference. Similarly, if the attribute_designator is for an attribute defined for (at least some) functions, then the prefix is never interpreted as a parameterless function_call; otherwise (and for all range_attribute_references), if the prefix consists of a name that denotes a function, it is interpreted as a parameterless function_call.

The expression, if any, in an attribute_designator or range_attribute_designator is expected to be of any integer type.

Legality Rules

The expression, if any, in an attribute_designator or range_attribute_designator shall be static.

Static Semantics

An attribute_reference denotes a value, an object, a subprogram, or some other kind of program entity.

A range_attribute_reference X'Range(N) is equivalent to the range X'First(N) .. X'Last(N), except that the prefix is only evaluated once. Similarly, X'Range is equivalent to X'First .. X'Last, except that the prefix is only evaluated once.

Dynamic Semantics

The evaluation of an attribute_reference (or range_attribute_reference) consists of the evaluation of the prefix.

Implementation Permissions

An implementation may provide implementation-defined attributes; the identifier for an implementation-defined attribute shall differ from those of the language-defined attributes unless supplied for compatibility with a previous edition of this International Standard.

Notes

4 Attributes are defined throughout this International Standard, and are summarized in Annex K.

5 In general, the name in a prefix of an attribute_reference (or a range_attribute_reference) has to be resolved without using any context. However, in the case of the Access attribute, the expected type for the prefix has to be a single access type, and if it is an access-to-subprogram type (see 3.10.2) then the resolution of the name can use the fact that the profile of the callable entity denoted by the prefix has to be type conformant with the designated profile of the access type.

Examples

Examples of attributes:

Color'First        -- minimum value of the enumeration type Color    (see 3.5.1) 
Rainbow'Base'First -- same as Color'First                            (see 3.5.1) 
Real'Digits        -- precision of the type Real                     (see 3.5.7) 
Board'Last(2)      -- upper bound of the second dimension of Board   (see 3.6.1) 
Board'Range(1)     -- index range of the first dimension of Board    (see 3.6.1) 
Pool(K)'Terminated -- True if task Pool(K) is terminated             (see 9.1) 
Date'Size          -- number of bits for records of type Date        (see 3.8) 
Message'Address    -- address of the record variable Message         (see 3.7.1)

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