13.12 Pragma Restrictions and Pragma Profile
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[A
pragma
Restrictions expresses the user's intent to abide by certain restrictions.
A
pragma Profile
expresses the user's intent to abide by a set of Restrictions or other
specified run-time policies. These may facilitate the construction of
simpler run-time environments.]
Syntax
The form of a
pragma
Restrictions is as follows:
Name Resolution Rules
Unless otherwise specified for
a particular restriction, the
expression
is expected to be of any integer type.
Legality Rules
Unless otherwise specified for a particular restriction,
the
expression
shall be static, and its value shall be nonnegative.
This paragraph
was deleted.
Paragraph 7 was deleted.
Post-Compilation Rules
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A
pragma
Restrictions is a configuration pragma. If a
pragma
Restrictions applies to any compilation unit included in the partition,
this may impose either (or both) of two kinds of requirements, as specified
for the particular restriction:
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A restriction may impose requirements on some or all of the units comprising
the partition. Unless otherwise specified for a particular restriction,
such a requirement applies to all of the units comprising the partition
and is enforced via a post-compilation check.
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A restriction may impose requirements on the run-time behavior of the
program, as indicated by the specification of run-time behavior associated
with a violation of the requirement.
Ramification: In this latter case, there
is no post-compilation check needed for the requirement.
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8652/0042}
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AI95-00130-01}
For the purpose of checking whether a partition contains constructs that
violate any restriction (unless specified otherwise for a particular
restriction):
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8652/0042}
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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;
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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
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An implementation may provide implementation-defined restrictions; the
identifier for an implementation-defined restriction shall differ from
those of the language-defined restrictions.
Implementation defined: Implementation-defined
restrictions allowed in a
pragma
Restrictions.
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.
Implementation defined: The consequences
of violating limitations on Restrictions
pragmas.
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.
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8652/0042}
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AI95-00130-01}
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.
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8652/0043}
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AI95-00190-01}
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.
Syntax
Legality Rules
Static Semantics
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A profile is equivalent to the set of configuration pragmas that is defined
for each usage profile.
Post-Compilation Rules
Implementation Permissions
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An implementation may provide implementation-defined usage profiles;
the identifier for an implementation-defined usage profile shall differ
from those of the language-defined usage profiles.
Implementation defined: Implementation-defined
usage profiles allowed in a
pragma
Profile.
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Restrictions intended to facilitate the construction of efficient tasking
run-time systems are defined in
D.7. Restrictions
intended for use when constructing high integrity systems are defined
in
H.4.
37 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.
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
Pragma Restrictions is new
to Ada 95.
Extensions to Ada 95
Wording Changes from Ada 95
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8652/0042}
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Corrigendum: Corrected the wording so that restrictions are checked
inside of generic instantiations and in default expressions. Since not
making these checks would violate the purpose of restrictions, we are
not documenting this as an incompatibility.
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8652/0043}
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AI95-00190-01}
Corrigendum: Added a permission that restrictions can be enforced
at compile-time. While this is technically incompatible, documenting
it as such would be unnecessarily alarming - there should not be any
programs depending on the runtime failure of restrictions.
Wording Changes from Ada 2005
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Correction: When restrictions are checked has been clarified.
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe
