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<H1> 12.6 Formal Subprograms</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> [<A NAME="I4303"></A> <A NAME="I4304"></A>Formal
subprograms can be used to pass callable entities to a generic unit.]
</DIV>
<H4 ALIGN=CENTER>Language Design Principles</H4>
<DIV Class="Paranum"><FONT SIZE=-2>1.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>Generic formal subprograms are
like renames of the <FONT FACE="Arial, Helvetica">explicit_generic_actual_parameter</FONT>.
</FONT></DIV>
<H4 ALIGN=CENTER>Syntax</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">formal_subprogram_declaration<A NAME="I4305"></A>
::= </FONT><B>with</B> <A NAME="I4306"></A><FONT FACE="Arial, Helvetica">subprogram_specification</FONT> [<B>is</B> <A NAME="I4307"></A><FONT FACE="Arial, Helvetica">subprogram_default</FONT>];</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">subprogram_default<A NAME="I4308"></A>
::= </FONT><A NAME="I4309"></A><FONT FACE="Arial, Helvetica">default_name</FONT> | <></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">default_name<A NAME="I4310"></A>
::= </FONT><A NAME="I4311"></A><FONT FACE="Arial, Helvetica">name</FONT></DIV>
<H4 ALIGN=CENTER>Name Resolution Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Normal"> <A NAME="I4312"></A>The expected profile for the
<FONT FACE="Arial, Helvetica">default_name</FONT>, if any, is that of
the formal subprogram. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>This rule,
unlike others in this clause, is observed at compile time of the <FONT FACE="Arial, Helvetica">generic_declaration</FONT>.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>The evaluation of the <FONT FACE="Arial, Helvetica">default_name</FONT>
takes place during the elaboration of each instantiation that uses the
default, as defined in <A HREF="AA-12-3.html">12.3</A>, ``<A HREF="AA-12-3.html">Generic
Instantiation</A>''. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Normal"> <A NAME="I4313"></A>For a generic formal subprogram,
the expected profile for the actual is that of the formal subprogram.
</DIV>
<H4 ALIGN=CENTER>Legality Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Normal"> The profiles of the formal and any named default
shall be mode-conformant. <A NAME="I4314"></A></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>This rule,
unlike others in this clause, is checked at compile time of the <FONT FACE="Arial, Helvetica">generic_declaration</FONT>.
</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Normal"> The profiles of the formal and actual shall be
mode-conformant. <A NAME="I4315"></A></DIV>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Normal"> A <FONT FACE="Arial, Helvetica">formal_subprogram_declaration</FONT>
declares a generic formal subprogram. The types of the formal parameters
and result, if any, of the formal subprogram are those determined by
the <FONT FACE="Arial, Helvetica">subtype_mark</FONT>s given in the <FONT FACE="Arial, Helvetica">formal_subprogram_declaration</FONT>;
however, independent of the particular subtypes that are denoted by the
<FONT FACE="Arial, Helvetica">subtype_mark</FONT>s, the nominal subtypes
of the formal parameters and result, if any, are defined to be nonstatic,
and unconstrained if of an array type [(no applicable index constraint
is provided in a call on a formal subprogram)]. In an instance, a <FONT FACE="Arial, Helvetica">formal_subprogram_declaration</FONT>
declares a view of the actual. The profile of this view takes its subtypes
and calling convention from the original profile of the actual entity,
while taking the formal parameter <FONT FACE="Arial, Helvetica">name</FONT>s
and <FONT FACE="Arial, Helvetica">default_expression</FONT>s from the
profile given in the <FONT FACE="Arial, Helvetica">formal_subprogram_declaration</FONT>.
The view is a function or procedure, never an entry. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>This rule is
intended to be the same as the one for renamings-as-declarations, where
the <FONT FACE="Arial, Helvetica">formal_subprogram_declaration</FONT>
is analogous to a renaming-as-declaration, and the actual is analogous
to the renamed view. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Normal"> If a generic unit has a <FONT FACE="Arial, Helvetica">subprogram_default</FONT>
specified by a box, and the corresponding actual parameter is omitted,
then it is equivalent to an explicit actual parameter that is a usage
name identical to the defining name of the formal. </DIV>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>13 The matching rules for
formal subprograms state requirements that are similar to those applying
to <FONT FACE="Arial, Helvetica">subprogram_renaming_declaration</FONT>s
(see <A HREF="AA-8-5-4.html">8.5.4</A>). In particular, the name of a
parameter of the formal subprogram need not be the same as that of the
corresponding parameter of the actual subprogram; similarly, for these
parameters, <FONT FACE="Arial, Helvetica">default_expression</FONT>s
need not correspond.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>14 The constraints that apply
to a parameter of a formal subprogram are those of the corresponding
formal parameter of the matching actual subprogram (not those implied
by the corresponding <FONT FACE="Arial, Helvetica">subtype_mark</FONT>
in the <FONT FACE="Arial, Helvetica">_specification</FONT> of the formal
subprogram). A similar remark applies to the result of a function. Therefore,
to avoid confusion, it is recommended that the <FONT FACE="Arial, Helvetica">name</FONT>
of a first subtype be used in any declaration of a formal subprogram.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>15 The subtype specified
for a formal parameter of a generic formal subprogram can be any visible
subtype, including a generic formal subtype of the same <FONT FACE="Arial, Helvetica">generic_formal_part</FONT>.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>14</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>16 A formal subprogram is
matched by an attribute of a type if the attribute is a function with
a matching specification. An enumeration literal of a given type matches
a parameterless formal function whose result type is the given type.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>15</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>17 A <FONT FACE="Arial, Helvetica">default_name</FONT>
denotes an entity that is visible or directly visible at the place of
the <FONT FACE="Arial, Helvetica">generic_declaration</FONT>; a box used
as a default is equivalent to a name that denotes an entity that is directly
visible at the place of the <FONT FACE="Arial, Helvetica">_instantiation</FONT>.
</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>15.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Proof: </B>Visibility and name
resolution are applied to the equivalent explicit actual parameter. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>16</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>18 The actual subprogram
cannot be abstract (see <A HREF="AA-3-9-3.html">3.9.3</A>). </FONT></DIV>
<H4 ALIGN=CENTER>Examples</H4>
<DIV Class="Paranum"><FONT SIZE=-2>17</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <I>Examples of
generic formal subprograms:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>18</FONT></DIV>
<DIV Class="Examples"><TT><B>with</B> <B>function</B> "+"(X, Y : Item) <B>return</B> Item <B>is</B> <>;<BR>
<B>with</B> <B>function</B> Image(X : Enum) <B>return</B> String <B>is</B> Enum'Image;<BR>
<B>with</B> <B>procedure</B> Update <B>is</B> Default_Update;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>19</FONT></DIV>
<DIV Class="Examples"><TT>--<I> given the generic procedure declaration </I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>20</FONT></DIV>
<DIV Class="Examples"><TT><B>generic</B><BR>
<B>with</B> <B>procedure</B> Action (X : <B>in</B> Item);<BR>
<B>procedure</B> Iterate(Seq : <B>in</B> Item_Sequence);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>21</FONT></DIV>
<DIV Class="Examples"><TT>--<I> and the procedure </I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>22</FONT></DIV>
<DIV Class="Examples"><TT><B>procedure</B> Put_Item(X : <B>in</B> Item);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>23</FONT></DIV>
<DIV Class="Examples"><TT>--<I> the following instantiation is possible </I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>24</FONT></DIV>
<DIV Class="Examples"><TT><B>procedure</B> Put_List <B>is</B> <B>new</B> Iterate(Action => Put_Item);</TT></DIV>
<HR>
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