4.1.4 Attributes
1
An
attribute is a characteristic
of an entity that can be queried via an
attribute_reference
or a
range_attribute_reference.
Syntax
2
attribute_reference ::= prefix'
attribute_designator
3
attribute_designator ::=
identifier[(
static_expression)]
| Access | Delta | Digits
4
range_attribute_reference ::= prefix'
range_attribute_designator
5
range_attribute_designator ::= Range[(
static_expression)]
Name Resolution Rules
6
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.
7
The
expression,
if any, in an
attribute_designator or
range_attribute_designator
is expected to be of any integer type.
Legality Rules
8
The expression, if any,
in an attribute_designator or range_attribute_designator
shall be static.
Static Semantics
9
An attribute_reference
denotes a value, an object, a subprogram, or some other kind of program
entity.
10
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
11
The evaluation
of an
attribute_reference (or
range_attribute_reference)
consists of the evaluation of the
prefix.
Implementation Permissions
12/1
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.
13
4 Attributes are defined throughout this
International Standard, and are summarized in
Annex
K.
14/2
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
attribute_reference
has to be a single access type, and the resolution of the
name
can use the fact that the type of the object or the profile of the callable
entity denoted by the
prefix has to match
the designated type or be type conformant with the designated profile
of the access type.
Examples
15
Examples of attributes:
16
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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