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<H1> 10.1.3 Subunits of Compilation Units</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> [Subunits are like child units, with these (important)
differences: subunits support the separate compilation of bodies only
(not declarations); the parent contains a <FONT FACE="Arial, Helvetica">body_stub</FONT>
to indicate the existence and place of each of its subunits; declarations
appearing in the parent's body can be visible within the subunits.] </DIV>
<H4 ALIGN=CENTER>Syntax</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">body_stub<A NAME="I3906"></A>
::= </FONT><A NAME="I3907"></A><FONT FACE="Arial, Helvetica">subprogram_body_stub</FONT> | <A NAME="I3908"></A><FONT FACE="Arial, Helvetica">package_body_stub</FONT> | <A NAME="I3909"></A><FONT FACE="Arial, Helvetica">task_body_stub</FONT> | <A NAME="I3910"></A><FONT FACE="Arial, Helvetica">protected_body_stub</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">subprogram_body_stub<A NAME="I3911"></A>
::= </FONT><A NAME="I3912"></A><FONT FACE="Arial, Helvetica">subprogram_specification</FONT> <B>is</B> <B>separate</B>;</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>Although this
syntax allows a <FONT FACE="Arial, Helvetica">parent_unit_name</FONT>,
that is disallowed by <A HREF="AA-10-1-1.html">10.1.1</A>, ``<A HREF="AA-10-1-1.html">Compilation
Units - Library Units</A>''. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">package_body_stub<A NAME="I3913"></A>
::= </FONT><B>package</B> <B>body</B> <A NAME="I3914"></A><FONT FACE="Arial, Helvetica">defining_identifier</FONT> <B>is</B> <B>separate</B>;</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">task_body_stub<A NAME="I3915"></A>
::= </FONT><B>task</B> <B>body</B> <A NAME="I3916"></A><FONT FACE="Arial, Helvetica">defining_identifier</FONT> <B>is</B> <B>separate</B>;</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">protected_body_stub<A NAME="I3917"></A>
::= </FONT><B>protected</B> <B>body</B> <A NAME="I3918"></A><FONT FACE="Arial, Helvetica">defining_identifier</FONT> <B>is</B> <B>separate</B>;</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">subunit<A NAME="I3919"></A>
::= </FONT><B>separate</B> (<A NAME="I3920"></A><FONT FACE="Arial, Helvetica">parent_unit_name</FONT>) <A NAME="I3921"></A><FONT FACE="Arial, Helvetica">proper_body</FONT></DIV>
<H4 ALIGN=CENTER>Legality Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3922"></A>The <I>parent body</I> of
a subunit is the body of the program unit denoted by its <FONT FACE="Arial, Helvetica">parent_unit_name</FONT>.
<A NAME="I3923"></A> The term <I>subunit</I> is used to refer to a <FONT FACE="Arial, Helvetica">subunit</FONT>
and also to the <FONT FACE="Arial, Helvetica">proper_body</FONT> of a
<FONT FACE="Arial, Helvetica">subunit</FONT>.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Normal"> The parent body of a subunit shall be present
in the current environment, and shall contain a corresponding <FONT FACE="Arial, Helvetica">body_stub</FONT>
with the same <FONT FACE="Arial, Helvetica">defining_identifier</FONT>
as the subunit. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>This can't
be a Name Resolution Rule, because a <FONT FACE="Arial, Helvetica">subunit</FONT>
is not a complete context. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Normal"> A <FONT FACE="Arial, Helvetica">package_body_stub</FONT>
shall be the completion of a <FONT FACE="Arial, Helvetica">package_declaration</FONT>
or <FONT FACE="Arial, Helvetica">generic_package_declaration</FONT>;
a <FONT FACE="Arial, Helvetica">task_body_stub</FONT> shall be the completion
of a <FONT FACE="Arial, Helvetica">task_declaration</FONT>; a <FONT FACE="Arial, Helvetica">protected_body_stub</FONT>
shall be the completion of a <FONT FACE="Arial, Helvetica">protected_declaration</FONT>.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Normal"> In contrast, a <FONT FACE="Arial, Helvetica">subprogram_body_stub</FONT>
need not be the completion of a previous declaration, [in which case
the <FONT FACE="Arial, Helvetica">_stub</FONT> declares the subprogram].
If the <FONT FACE="Arial, Helvetica">_stub</FONT> is a completion, it
shall be the completion of a <FONT FACE="Arial, Helvetica">subprogram_declaration</FONT>
or <FONT FACE="Arial, Helvetica">generic_subprogram_declaration</FONT>.
The profile of a <FONT FACE="Arial, Helvetica">subprogram_body_stub</FONT>
that completes a declaration shall conform fully to that of the declaration.
<A NAME="I3924"></A></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>11.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>The part about
<FONT FACE="Arial, Helvetica">subprogram_body_stub</FONT>s echoes the
corresponding rule for <FONT FACE="Arial, Helvetica">subprogram_bodies</FONT>
in <A HREF="AA-6-3.html">6.3</A>, ``<A HREF="AA-6-3.html">Subprogram
Bodies</A>''. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DIV Class="Normal"> A subunit that corresponds to a <FONT FACE="Arial, Helvetica">body_stub</FONT>
shall be of the same kind (<FONT FACE="Arial, Helvetica">package_</FONT>,
<FONT FACE="Arial, Helvetica">subprogram_</FONT>, <FONT FACE="Arial, Helvetica">task_</FONT>,
or <FONT FACE="Arial, Helvetica">protected_</FONT>) as the <FONT FACE="Arial, Helvetica">body_stub</FONT>.
The profile of a <FONT FACE="Arial, Helvetica">subprogram_body</FONT>
subunit shall be fully conformant to that of the corresponding <FONT FACE="Arial, Helvetica">body_stub</FONT>.
<A NAME="I3925"></A></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13</FONT></DIV>
<DIV Class="Normal"> A <FONT FACE="Arial, Helvetica">body_stub</FONT>
shall appear immediately within the <FONT FACE="Arial, Helvetica">declarative_part</FONT>
of a compilation unit body. This rule does not apply within an instance
of a generic unit. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B><A NAME="I3926"></A>This
is a methodological restriction; that is, it is not necessary for the
semantics of the language to make sense. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>14</FONT></DIV>
<DIV Class="Normal"> The <FONT FACE="Arial, Helvetica">defining_identifier</FONT>s
of all <FONT FACE="Arial, Helvetica">body_stub</FONT>s that appear immediately
within a particular <FONT FACE="Arial, Helvetica">declarative_part</FONT>
shall be distinct. </DIV>
<H4 ALIGN=CENTER>Post-Compilation Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>15</FONT></DIV>
<DIV Class="Normal"> For each <FONT FACE="Arial, Helvetica">body_stub</FONT>,
there shall be a subunit containing the corresponding <FONT FACE="Arial, Helvetica">proper_body</FONT>.
</DIV>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>16</FONT></DIV>
<DIV Class="Notes" Style="margin-bottom: 0.4em"><FONT SIZE=-1>4 The
rules in <A HREF="AA-10-1-4.html">10.1.4</A>, ``<A HREF="AA-10-1-4.html">The
Compilation Process</A>'' say that a <FONT FACE="Arial, Helvetica">body_stub</FONT>
is equivalent to the corresponding <FONT FACE="Arial, Helvetica">proper_body</FONT>.
This implies: </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>17</FONT></DIV>
<UL Class="NotesBulleted"><FONT SIZE=-1><LI TYPE=DISC>Visibility within a subunit is the visibility that would
be obtained at the place of the corresponding <FONT FACE="Arial, Helvetica">body_stub</FONT>
(within the parent body) if the <FONT FACE="Arial, Helvetica">context_clause</FONT>
of the subunit were appended to that of the parent body. </LI></FONT></UL>
<DIV Class="Paranum"><FONT SIZE=-2>17.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>Recursively.
Note that this transformation might make the parent illegal; hence it
is not a true equivalence, but applies only to visibility within the
subunit. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>18</FONT></DIV>
<UL Class="NotesBulleted"><FONT SIZE=-1><LI TYPE=DISC>The effect of the elaboration of a <FONT FACE="Arial, Helvetica">body_stub</FONT>
is to elaborate the subunit. </LI></FONT></UL>
<DIV Class="Paranum"><FONT SIZE=-2>18.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>The elaboration
of a subunit is part of its parent body's elaboration, whereas the elaboration
of a child unit is not part of its parent declaration's elaboration.
</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>18.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>A <FONT FACE="Arial, Helvetica">library_item</FONT>
that is mentioned in a <FONT FACE="Arial, Helvetica">with_clause</FONT>
of a subunit can be hidden (from direct visiblity) by a declaration (with
the same <FONT FACE="Arial, Helvetica">identifier</FONT>) given in the
subunit. Moreover, such a <FONT FACE="Arial, Helvetica">library_item</FONT>
can even be hidden by a declaration given within the parent body since
a library unit is declared in its parent's declarative region; this however
does not affect the interpretation of the <FONT FACE="Arial, Helvetica">with_clause</FONT>s
themselves, since only <FONT FACE="Arial, Helvetica">library_item</FONT>s
are visible or directly visible in <FONT FACE="Arial, Helvetica">with_clause</FONT>s.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>18.c</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>The body of a protected operation
cannot be a subunit. This follows from the syntax rules. The body of
a protected unit can be a subunit. </FONT></DIV>
<H4 ALIGN=CENTER>Examples</H4>
<DIV Class="Paranum"><FONT SIZE=-2>19</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> The package Parent
is first written without subunits: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>20</FONT></DIV>
<DIV Class="Examples"><TT><B>package</B> Parent <B>is</B><BR>
<B>procedure</B> Inner;<BR>
<B>end</B> Parent;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>21</FONT></DIV>
<DIV Class="Examples"><TT><B>with</B> Ada.Text_IO;<BR>
<B>package</B> <B>body</B> Parent <B>is</B><BR>
Variable : String := "Hello, there.";<BR>
<B>procedure</B> Inner <B>is</B><BR>
<B>begin</B><BR>
Ada.Text_IO.Put_Line(Variable);<BR>
<B>end</B> Inner;<BR>
<B>end</B> Parent;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>22</FONT></DIV>
<DIV Class="Wide" Style="margin-bottom: 0.4em"> The body of procedure
Inner may be turned into a subunit by rewriting the package body as follows
(with the declaration of Parent remaining the same): </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>23</FONT></DIV>
<DIV Class="Examples"><TT><B>package</B> <B>body</B> Parent <B>is</B><BR>
Variable : String := "Hello, there.";<BR>
<B>procedure</B> Inner <B>is</B> <B>separate</B>;<BR>
<B>end</B> Parent;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>24</FONT></DIV>
<DIV Class="Examples"><TT><B>with</B> Ada.Text_IO;<BR>
<B>separate</B>(Parent)<BR>
<B>procedure</B> Inner <B>is</B><BR>
<B>begin</B><BR>
Ada.Text_IO.Put_Line(Variable);<BR>
<B>end</B> Inner;</TT></DIV>
<H4 ALIGN=CENTER>Extensions to Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>24.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><A NAME="I3927"></A>Subunits of
the same ancestor library unit are no longer restricted to have distinct
identifiers. Instead, we require only that the full expanded names be
distinct. </FONT></DIV>
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