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<H1> 4.7 Qualified Expressions</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> [A <FONT FACE="Arial, Helvetica">qualified_expression</FONT>
is used to state explicitly the type, and to verify the subtype, of an
operand that is either an <FONT FACE="Arial, Helvetica">expression</FONT>
or an <FONT FACE="Arial, Helvetica">aggregate</FONT>. <A NAME="I2815"></A>]</DIV>
<H4 ALIGN=CENTER>Syntax</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">qualified_expression<A NAME="I2816"></A>
::= </FONT><BR>
<A NAME="I2817"></A><FONT FACE="Arial, Helvetica">subtype_mark</FONT>'(<A NAME="I2818"></A><FONT FACE="Arial, Helvetica">expression</FONT>) | <A NAME="I2819"></A><FONT FACE="Arial, Helvetica">subtype_mark</FONT>'<A NAME="I2820"></A><FONT FACE="Arial, Helvetica">aggregate</FONT></DIV>
<H4 ALIGN=CENTER>Name Resolution Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="Normal"> <A NAME="I2821"></A>The <I>operand</I> (the <FONT FACE="Arial, Helvetica">expression</FONT>
or <FONT FACE="Arial, Helvetica">aggregate</FONT>) shall resolve to be
of the type determined by the <FONT FACE="Arial, Helvetica">subtype_mark</FONT>,
or a universal type that covers it. </DIV>
<H4 ALIGN=CENTER>Dynamic Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Normal"> <A NAME="I2822"></A><A NAME="I2823"></A><A NAME="I2824"></A><A NAME="I2825"></A><A NAME="I2826"></A><A NAME="I2827"></A><A NAME="I2828"></A>The
evaluation of a <FONT FACE="Arial, Helvetica">qualified_expression</FONT>
evaluates the operand (and if of a universal type, converts it to the
type determined by the <FONT FACE="Arial, Helvetica">subtype_mark</FONT>)
and checks that its value belongs to the subtype denoted by the <FONT FACE="Arial, Helvetica">subtype_mark</FONT>.
<A NAME="I2829"></A><A NAME="I2830"></A>The exception Constraint_Error
is raised if this check fails. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>This is one
of the few contexts in Ada 95 where implicit subtype conversion is not
performed prior to a constraint check, and hence no ``sliding'' of array
bounds is provided. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Reason: </B>Implicit subtype
conversion is not provided because a <FONT FACE="Arial, Helvetica">qualified_expression</FONT>
with a constrained target subtype is essentially an assertion about the
subtype of the operand, rather than a request for conversion. An explicit
<FONT FACE="Arial, Helvetica">type_conversion</FONT> can be used rather
than a <FONT FACE="Arial, Helvetica">qualified_expression</FONT> if subtype
conversion is desired. </FONT></DIV>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>23 When a given context does
not uniquely identify an expected type, a <FONT FACE="Arial, Helvetica">qualified_expression</FONT>
can be used to do so. In particular, if an overloaded <FONT FACE="Arial, Helvetica">name</FONT>
or <FONT FACE="Arial, Helvetica">aggregate</FONT> is passed to an overloaded
subprogram, it might be necessary to qualify the operand to resolve its
type. </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>Examples of disambiguating
expressions using qualification:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Examples"><TT><B>type</B> Mask <B>is</B> (Fix, Dec, Exp, Signif);<BR>
<B>type</B> Code <B>is</B> (Fix, Cla, Dec, Tnz, Sub);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Examples"><TT>Print (Mask'(Dec)); <I>-- Dec is of type Mask</I><BR>
Print (Code'(Dec)); <I>-- Dec is of type Code </I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Examples"><TT><B>for</B> J <B>in</B> Code'(Fix) .. Code'(Dec) <B>loop</B> ... <I>-- qualification needed for either Fix or Dec</I><BR>
<B>for</B> J <B>in</B> Code <B>range</B> Fix .. Dec <B>loop</B> ... <I>-- qualification unnecessary</I><BR>
<B>for</B> J <B>in</B> Code'(Fix) .. Dec <B>loop</B> ... <I>-- qualification unnecessary for Dec</I></TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Examples"><TT>Dozen'(1 | 3 | 5 | 7 => 2, <B>others</B> => 0) <I>-- see <A HREF="AA-4-6.html">4.6</A> </I></TT></DIV>
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