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<H1> 13.12 Pragma Restrictions</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> [A <FONT FACE="Arial, Helvetica">pragma</FONT>
Restrictions expresses the user's intent to abide by certain restrictions.
This may facilitate the construction of simpler run-time environments.]
</DIV>
<H4 ALIGN=CENTER>Syntax</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="SyntaxIndented" Style="margin-bottom: 0.2em">The form of
a <FONT FACE="Arial, Helvetica">pragma</FONT> Restrictions is as follows:
</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="SyntaxIndented"> <B>pragma</B> <A NAME="I4691"></A>Restrictions(<A NAME="I4692"></A><FONT FACE="Arial, Helvetica">restriction</FONT>{,
<A NAME="I4693"></A><FONT FACE="Arial, Helvetica">restriction</FONT>});</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">restriction<A NAME="I4694"></A>
::= </FONT><I>restriction_</I><A NAME="I4695"></A><FONT FACE="Arial, Helvetica">identifier</FONT><BR>
| <I>restriction_parameter_</I><A NAME="I4696"></A><FONT FACE="Arial, Helvetica">identifier</FONT> => <A NAME="I4697"></A><FONT FACE="Arial, Helvetica">expression</FONT></DIV>
<H4 ALIGN=CENTER>Name Resolution Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Normal"> <A NAME="I4698"></A>Unless otherwise specified
for a particular restriction, the <FONT FACE="Arial, Helvetica">expression</FONT>
is expected to be of any integer type. </DIV>
<H4 ALIGN=CENTER>Legality Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Normal"> Unless otherwise specified for a particular restriction,
the <FONT FACE="Arial, Helvetica">expression</FONT> shall be static,
and its value shall be nonnegative. </DIV>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Normal"> The set of <FONT FACE="Arial, Helvetica">restrictions</FONT>
is implementation defined. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Implementation defined: </B>The
set of <FONT FACE="Arial, Helvetica">restrictions</FONT> allowed in a
<FONT FACE="Arial, Helvetica">pragma</FONT> Restrictions.</FONT></DIV>
<H4 ALIGN=CENTER>Post-Compilation Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Normal"> <A NAME="I4699"></A><A NAME="I4700"></A>A <FONT FACE="Arial, Helvetica">pragma</FONT>
Restrictions is a configuration pragma; unless otherwise specified for
a particular restriction, a partition shall obey the restriction if a
<FONT FACE="Arial, Helvetica">pragma</FONT> Restrictions applies to any
compilation unit included in the partition.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8.1/1</FONT></DIV>
<DIV Class="Normal"> {<I><A HREF="defect1.html#8652/0042">8652/0042</A></I>}
<U>For the purpose of checking whether a partition contains constructs
that violate any restriction (unless specified otherwise for a particular
restriction):</U></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8.2/1</FONT></DIV>
<UL Class="Bulleted" Style="margin-bottom: 0.3em"><LI TYPE=DISC>{<I><A HREF="defect1.html#8652/0042">8652/0042</A></I>}
<U>Generic instances are logically expanded at the point of instantiation;</U></LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>8.3/1</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>{<I><A HREF="defect1.html#8652/0042">8652/0042</A></I>}
<U>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;</U></LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>8.4/1</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>{<I><A HREF="defect1.html#8652/0042">8652/0042</A></I>}
<U>A <FONT FACE="Arial, Helvetica">default_expression</FONT> 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.</U> </LI></UL>
<H4 ALIGN=CENTER>Implementation Permissions</H4>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Normal"> An implementation may place limitations on the
values of the <FONT FACE="Arial, Helvetica">expression</FONT> that are
supported, and limitations on the supported combinations of restrictions.
The consequences of violating such limitations are implementation defined.
</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Implementation defined: </B>The
consequences of violating limitations on Restrictions <FONT FACE="Arial, Helvetica">pragma</FONT>s.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>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. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9.1/1</FONT></DIV>
<DIV Class="Normal"> {<I><A HREF="defect1.html#8652/0042">8652/0042</A></I>}
<U>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.</U></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9.2/1</FONT></DIV>
<DIV Class="Normal"> {<I><A HREF="defect1.html#8652/0043">8652/0043</A></I>}
<U>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.</U> </DIV>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>28 Restrictions intended
to facilitate the construction of efficient tasking run-time systems
are defined in <A HREF="AA-D-7.html">D.7</A>. Safety- and security-related
restrictions are defined in <A HREF="AA-H-4.html">H.4</A>.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>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.
</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>11.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>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. </FONT></DIV>
<H4 ALIGN=CENTER>Extensions to Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>11.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><A NAME="I4701"></A>Pragma Restrictions
is new to Ada 95. </FONT></DIV>
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