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<H1> 12.5.4 Formal Access Types</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> [The class determined for a formal access type
is the class of all access types.] </DIV>
<H4 ALIGN=CENTER>Syntax</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">formal_access_type_definition<A NAME="I4297"></A>
::= </FONT><A NAME="I4298"></A><FONT FACE="Arial, Helvetica">access_type_definition</FONT></DIV>
<H4 ALIGN=CENTER>Legality Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="Normal"> For a formal access-to-object type, the designated
subtypes of the formal and actual types shall statically match. <A NAME="I4299"></A></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Normal"> If and only if the <FONT FACE="Arial, Helvetica">general_access_modifier</FONT>
<B>constant</B> applies to the formal, the actual shall be an access-to-constant
type. If the <FONT FACE="Arial, Helvetica">general_access_modifier</FONT>
<B>all</B> applies to the formal, then the actual shall be a general
access-to-variable type (see <A HREF="AA-3-10.html">3.10</A>). </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>If no <FONT FACE="Arial, Helvetica">_modifier</FONT>
applies to the formal, then the actual type may be either a pool-specific
or a general access-to-variable type. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4.a.1/1</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Reason: </B>{<I><A HREF="defect2.html#8652/0109">8652/0109</A></I>}
<U>Matching an access-to-variable to a formal access-to-constant type
cannot be allowed. If it were allowed, it would be possible to create
an access-to-variable value designating a constant.</U> </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Normal"> For a formal access-to-subprogram subtype, the
designated profiles of the formal and the actual shall be mode-conformant,
and the calling convention of the actual shall be <I>protected</I> if
and only if that of the formal is <I>protected</I>. <A NAME="I4300"></A></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Reason: </B>We considered requiring
subtype conformance here, but mode conformance is more flexible, given
that there is no way in general to specify the convention of the formal.
</FONT></DIV>
<H4 ALIGN=CENTER>Examples</H4>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <I>Example of formal
access types:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Examples"><TT>--<I> the formal types of the generic package </I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Examples"><TT><B>generic</B><BR>
<B>type</B> Node <B>is</B> <B>private</B>;<BR>
<B>type</B> Link <B>is</B> <B>access</B> Node;<BR>
<B>package</B> P <B>is</B><BR>
...<BR>
<B>end</B> P;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Examples"><TT>--<I> can be matched by the actual types </I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Examples"><TT><B>type</B> Car;<BR>
<B>type</B> Car_Name <B>is</B> <B>access</B> Car;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Examples"><TT><B>type</B> Car <B>is</B><BR>
<B>record</B><BR>
Pred, Succ : Car_Name;<BR>
Number : License_Number;<BR>
Owner : Person;<BR>
<B>end</B> <B>record</B>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DIV Class="Examples"><TT>--<I> in the following generic instantiation </I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13</FONT></DIV>
<DIV Class="Examples"><TT><B>package</B> R <B>is</B> <B>new</B> P(Node => Car, Link => Car_Name);</TT></DIV>
<H4 ALIGN=CENTER>Incompatibilities With Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>13.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><A NAME="I4301"></A>The check
for matching of designated subtypes is changed from a run-time check
to a compile-time check. The Ada 83 rule that ``If the designated type
is other than a scalar type, then the designated subtypes shall be either
both constrained or both unconstrained'' is removed, since it is subsumed
by static matching. </FONT></DIV>
<H4 ALIGN=CENTER>Extensions to Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>13.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><A NAME="I4302"></A>Formal access-to-subprogram
subtypes and formal general access types are new concepts. </FONT></DIV>
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