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<H1> 7.4 Deferred Constants</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> Deferred constant declarations may be used to
declare constants in the visible part of a package, but with the value
of the constant given in the private part. They may also be used to declare
constants imported from other languages (see <A HREF="RM-B.html">Annex
B</A>). </DIV>
<H4 ALIGN=CENTER>Legality Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3103"></A>A <I>deferred constant declaration</I>
is an <FONT FACE="Arial, Helvetica">object_declaration</FONT> with the
reserved word <B>constant</B> but no initialization expression. <A NAME="I3104"></A>The
constant declared by a deferred constant declaration is called a <I>deferred
constant</I>. <A NAME="I3105"></A>A deferred constant declaration requires
a completion, which shall be a full constant declaration (called the
<I>full declaration</I> of the deferred constant), or a <FONT FACE="Arial, Helvetica">pragma</FONT>
Import (see <A HREF="RM-B.html">Annex B</A>). <A NAME="I3106"></A></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> A deferred constant
declaration that is completed by a full constant declaration shall occur
immediately within the visible part of a <FONT FACE="Arial, Helvetica">package_specification</FONT>.
For this case, the following additional rules apply to the corresponding
full declaration: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>The full declaration shall occur immediately within the
private part of the same package;</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>The deferred and full constants shall have the same type;
</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>If the subtype defined by the <FONT FACE="Arial, Helvetica">subtype_indication</FONT>
in the deferred declaration is constrained, then the subtype defined
by the <FONT FACE="Arial, Helvetica">subtype_indication</FONT> in the
full declaration shall match it statically. On the other hand, if the
subtype of the deferred constant is unconstrained, then the full declaration
is still allowed to impose a constraint. The constant itself will be
constrained, like all constants;</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>If the deferred constant declaration includes the reserved
word <B>aliased</B>, then the full declaration shall also. </LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Normal"> A deferred constant declaration that is completed
by a <FONT FACE="Arial, Helvetica">pragma</FONT> Import need not appear
in the visible part of a <FONT FACE="Arial, Helvetica">package_specification</FONT>,
and has no full constant declaration.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Normal"> The completion of a deferred constant declaration
shall occur before the constant is frozen (see <A HREF="RM-7-4.html">7.4</A>).</DIV>
<H4 ALIGN=CENTER>Dynamic Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3107"></A>The elaboration of a deferred
constant declaration elaborates the <FONT FACE="Arial, Helvetica">subtype_indication</FONT>
or (only allowed in the case of an imported constant) the <FONT FACE="Arial, Helvetica">array_type_definition</FONT>.
</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>12 The full constant declaration
for a deferred constant that is of a given private type or private extension
is not allowed before the corresponding <FONT FACE="Arial, Helvetica">full_type_declaration</FONT>.
This is a consequence of the freezing rules for types (see <A HREF="RM-13-14.html">13.14</A>).
</FONT></DIV>
<H4 ALIGN=CENTER>Examples</H4>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <I>Examples of
deferred constant declarations:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13</FONT></DIV>
<DIV Class="Examples"><TT>Null_Key : <B>constant</B> Key; <I>-- see <A HREF="RM-7-3-1.html">7.3.1</A></I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>14</FONT></DIV>
<DIV Class="Examples"><TT>CPU_Identifier : <B>constant</B> String(1..8);<BR>
<B>pragma</B> Import(Assembler, CPU_Identifier, Link_Name => "CPU_ID");<BR>
<I>-- see <A HREF="RM-B-1.html">B.1</A></I></TT></DIV>
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