C.5 Aspect Discard_NamesPragma Discard_Names
{
AI12-0072-1}
[
Specifying the aspect A
pragma
Discard_Names
can may
be used to request a reduction in storage used for the names of
certain
entities
with runtime name text.]
Static Semantics
{
AI12-0072-1}
An entity with runtime name text is a nonderived
enumeration first subtype, a tagged first subtype, or an exception. {
AI12-0072-1}
For an entity with runtime name text, the following
language-defined representation aspect may be specified: Discard_Names
The type of aspect Discard_Names is Boolean. If
directly specified, the aspect_definition
shall be a static expression. If not specified (including by inheritance),
the aspect is False.
Aspect Description
for Discard_Names: Requests
a reduction in storage for names associated with an entity.
Syntax
The form of a
pragma
Discard_Names is as follows:
Legality Rules
{
AI12-0072-1}
The
local_name
(if present) shall denote
an entity with runtime
name text a nonderived enumeration [first]
subtype, a tagged [first] subtype, or an exception. The pragma
specifies that the aspect Discard_Names for applies
to the type or exception
has the value True.
Without a
local_name,
the pragma
specifies that applies
to all
such entities
with runtime name text declared after the pragma, within the same
declarative region
have the value True for aspect
Discard_Names. Alternatively, the pragma can be used as a configuration
pragma.
If the configuration pragma Discard_Names
applies to a compilation unit, all entities with runtime name text declared
in the compilation unit have the value True for the aspect Discard_Names If
the pragma applies to a type, then it applies also to all descendants
of the type.
Ramification: {
AI12-0072-1}
If the aspect is specified for a type, then it
is inherited by all descendants of the type. The aspect cannot be specified
as False on a derived type (because specifying the aspect is not allowed
on derived enumeration types, and by rule applying to all aspects for
other types (see 13.1.1)).
Static Semantics
If a
local_name
is given, then a
pragma
Discard_Names is a representation pragma.
This paragraph
was deleted.Ramification: {
AI05-0229-1}
{
AI12-0072-1}
Representation pragmas automatically specify aspects
of the same name, so Discard_Names can be used as an aspect_mark
in an aspect_specification
instead of using the pragma on individual entities.
{
AI95-00285-01}
{
AI95-00400-01}
{
AI12-0072-1}
If the
aspect Discard_Names is True for pragma
applies to an enumeration type, then the semantics of the Wide_Wide_Image
and Wide_Wide_Value attributes are implementation defined for that type[;
the semantics of Image, Wide_Image, Value, and Wide_Value are still defined
in terms of Wide_Wide_Image and Wide_Wide_Value]. In addition, the semantics
of Text_IO.Enumeration_IO are implementation defined. If the
aspect
Discard_Names is True for pragma applies
to a tagged type, then the semantics of the Tags.Wide_Wide_Expanded_Name
function are implementation defined for that type[; the semantics of
Tags.Expanded_Name and Tags.Wide_Expanded_Name are still defined in terms
of Tags.Wide_Wide_Expanded_Name]. If the
aspect
Discard_Names is True for pragma applies
to an exception, then the semantics of the Exceptions.Wide_Wide_Exception_Name
function are implementation defined for that exception[; the semantics
of Exceptions.Exception_Name and Exceptions.Wide_Exception_Name are still
defined in terms of Exceptions.Wide_Wide_Exception_Name].
Implementation defined: The semantics
of some attributes and functions of an entity for
which aspect pragma Discard_Names is True.
Ramification: The Width attribute is
still defined in terms of Image.
{
AI95-00285-01}
{
AI12-0072-1}
The semantics of S'Wide_Wide_Image and S'Wide_Wide_Value are implementation
defined for any subtype of an enumeration type
for to
which the
aspect is True pragma
applies. (The pragma
, if used, actually
names the first subtype, of course.)
Implementation Advice
{
AI12-0072-1}
If the
aspect Discard_Names is True for pragma
applies to an entity, then the implementation should reduce the
amount of storage used for storing names associated with that entity.
Implementation Advice: If
aspect pragma
Discard_Names
is True for applies
to an entity, then the amount of storage used for storing names
associated with that entity should be reduced.
Reason: A typical implementation of the
Image attribute for enumeration types is to store a table containing
the names of all the enumeration literals. Aspect Pragma
Discard_Names allows the implementation to avoid storing such a table
without having to prove that the Image attribute is never used (which
can be difficult in the presence of separate compilation).
We did not specify the semantics of the Image
attribute when aspect Discard_Names is True in
the presence of this pragma because different semantics might
be desirable in different situations. In some cases, it might make sense
to use the Image attribute to print out a useful value that can be used
to identify the entity given information in compiler-generated listings.
In other cases, it might make sense to get an error at compile time or
at run time. In cases where memory is plentiful, the simplest implementation
makes sense: ignore the aspect pragma.
Implementations that are capable of avoiding the extra storage in cases
where the Image attribute is never used might also wish to ignore the
aspect pragma.
The same applies to the Tags.Expanded_Name and
Exceptions.Exception_Name functions.
Wording Changes from Ada 95
{
AI95-00285-01}
{
AI95-00400-01}
Updated the wording to reflect that the double wide image and value functions
are now the master versions that the others are defined from.
Wording Changes from Ada 2012
{
AI12-0072-1}
Corrigendum: Defined the pragma in terms
of the aspect Discard_Names, and added a missing definition of the meaning
of the configuration pragma. This is not intended to make any semantic
change (Ada 2012 has an aspect Discard_Names defined via blanket rules
for representation pragmas in 13.1 and 13.1.1),
just to clarify the meaning.
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe
