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<H1> 3.3.2 Number Declarations</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> A <FONT FACE="Arial, Helvetica">number_declaration</FONT>
declares a named number. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>1.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B><A NAME="I1485"></A>If
a value or other property of a construct is required to be <I>static</I>
that means it is required to be determined prior to execution. A <I>static</I>
expression is an expression whose value is computed at compile time and
is usable in contexts where the actual value might affect the legality
of the construct. This is fully defined in clause <A HREF="AA-4-9.html">4.9</A>.
</FONT></DIV>
<H4 ALIGN=CENTER>Syntax</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">number_declaration<A NAME="I1486"></A>
::= </FONT><BR>
<A NAME="I1487"></A><FONT FACE="Arial, Helvetica">defining_identifier_list</FONT> : <B>constant</B> := <I>static_</I><A NAME="I1488"></A><FONT FACE="Arial, Helvetica">expression</FONT>;</DIV>
<H4 ALIGN=CENTER>Name Resolution Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="Normal"> <A NAME="I1489"></A>The <I>static_</I><FONT FACE="Arial, Helvetica">expression</FONT>
given for a <FONT FACE="Arial, Helvetica">number_declaration</FONT> is
expected to be of any numeric type. </DIV>
<H4 ALIGN=CENTER>Legality Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Normal"> The <I>static_</I><FONT FACE="Arial, Helvetica">expression</FONT>
given for a number declaration shall be a static expression, as defined
by clause <A HREF="AA-4-9.html">4.9</A>. </DIV>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Normal"> The named number denotes a value of type <I>universal_integer</I>
if the type of the <I>static_</I><FONT FACE="Arial, Helvetica">expression</FONT>
is an integer type. The named number denotes a value of type <I>universal_real</I>
if the type of the <I>static_</I><FONT FACE="Arial, Helvetica">expression</FONT>
is a real type.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Normal"> The value denoted by the named number is the value
of the <I>static_</I><FONT FACE="Arial, Helvetica">expression</FONT>,
converted to the corresponding universal type. <A NAME="I1490"></A></DIV>
<H4 ALIGN=CENTER>Dynamic Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Normal"> <A NAME="I1491"></A>The elaboration of a <FONT FACE="Arial, Helvetica">number_declaration</FONT>
has no effect. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Proof: </B>Since the <I>static_</I><FONT FACE="Arial, Helvetica">expression</FONT>
was evaluated at compile time. </FONT></DIV>
<H4 ALIGN=CENTER>Examples</H4>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <I>Examples of number
declarations:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Examples"><TT>Two_Pi : <B>constant</B> := 2.0*Ada.Numerics.Pi; <I>-- a real number (see <A HREF="AA-A-5.html">A.5</A>)</I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Examples"><TT>Max : <B>constant</B> := 500; <I>-- an integer number</I><BR>
Max_Line_Size : <B>constant</B> := Max/6 <I>-- the integer 83</I><BR>
Power_16 : <B>constant</B> := 2**16; <I>-- the integer 65_536</I><BR>
One, Un, Eins : <B>constant</B> := 1; <I>-- three different names for 1</I></TT></DIV>
<H4 ALIGN=CENTER>Extensions to Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>10.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><A NAME="I1492"></A>We now allow
a static expression of any numeric type to initialize a named number.
For integer types, it was possible in Ada 83 to use 'Pos to define a
named number, but there was no way to use a static expression of some
non-universal real type to define a named number. This change is upward
compatible because of the preference rule for the operators of the root
numeric types. </FONT></DIV>
<H4 ALIGN=CENTER>Wording Changes from Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>10.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>We have moved the syntax rule
into this subclause.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10.c</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>AI83-00263 describes the elaboration
of a number declaration in words similar to that of an <FONT FACE="Arial, Helvetica">object_declaration</FONT>.
However, since there is no expression to be evaluated and no object to
be created, it seems simpler to say that the elaboration has no effect.
</FONT></DIV>
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