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13.12 Pragma Restrictions
1
[A pragma
Restrictions expresses the user's intent to abide by certain restrictions.
This may facilitate the construction of simpler run-time environments.]
Syntax
2
The form of
a pragma Restrictions is as follows:
3
pragma Restrictions(
restriction{,
restriction});
4
restriction
::= restriction_identifier
|
restriction_parameter_identifier =>
expression
Name Resolution Rules
5
{expected type (restriction
parameter expression) [partial]} Unless
otherwise specified for a particular restriction, the
expression
is expected to be of any integer type.
Legality Rules
6
Unless otherwise specified for a particular restriction,
the expression shall be static,
and its value shall be nonnegative.
Static Semantics
7
The set of restrictions
is implementation defined.
7.a
Implementation defined: The
set of restrictions allowed in a
pragma Restrictions.
Post-Compilation Rules
8
{configuration pragma (Restrictions)
[partial]} {pragma, configuration
(Restrictions) [partial]} A
pragma
Restrictions is a configuration pragma; unless otherwise specified for
a particular restriction, a partition shall obey the restriction if a
pragma Restrictions applies to any
compilation unit included in the partition.
8.1/1
{
8652/0042}
For the purpose of checking whether a partition contains constructs
that violate any restriction (unless specified otherwise for a particular
restriction): 8.2/1
- {8652/0042}
Generic instances are logically expanded at the point of instantiation;
8.3/1
- {8652/0042}
If an object of a type is declared or allocated and not explicitly
initialized, then all expressions appearing in the definition for the
type and any of its ancestors are presumed to be used;
8.4/1
- {8652/0042}
A default_expression for a formal
parameter or a generic formal object is considered to be used if and
only if the corresponding actual parameter is not provided in a given
call or instantiation.
Implementation Permissions
9
An implementation may place limitations on the
values of the expression that are
supported, and limitations on the supported combinations of restrictions.
The consequences of violating such limitations are implementation defined.
9.a
Implementation defined: The
consequences of violating limitations on Restrictions pragmas.
9.b
Ramification: Such limitations
may be enforced at compile time or at run time. Alternatively, the implementation
is allowed to declare violations of the restrictions to be erroneous,
and not enforce them at all.
9.1/1
{
8652/0042}
An implementation is permitted to omit restriction checks for code
that is recognized at compile time to be unreachable and for which no
code is generated. 9.2/1
{
8652/0043}
Whenever enforcement of a restriction is not required prior to execution,
an implementation may nevertheless enforce the restriction prior to execution
of a partition to which the restriction applies, provided that every
execution of the partition would violate the restriction. 10
28 Restrictions intended
to facilitate the construction of efficient tasking run-time systems
are defined in D.7. Safety- and security-related
restrictions are defined in H.4.
11
29 An implementation has
to enforce the restrictions in cases where enforcement is required, even
if it chooses not to take advantage of the restrictions in terms of efficiency.
11.a
Discussion: It is not
the intent that an implementation will support a different run-time system
for every possible combination of restrictions. An implementation might
support only two run-time systems, and document a set of restrictions
that is sufficient to allow use of the more efficient and safe one.
Extensions to Ada 83
11.b
{extensions to Ada 83}
Pragma Restrictions is new to Ada 95.
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