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<H1> 6.6 Overloading of Operators</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3182"></A><A NAME="I3183"></A><A NAME="I3184"></A>An
<I>operator</I> is a function whose <FONT FACE="Arial, Helvetica">designator</FONT>
is an <FONT FACE="Arial, Helvetica">operator_symbol</FONT>. [Operators,
like other functions, may be overloaded.] </DIV>
<H4 ALIGN=CENTER>Name Resolution Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="Normal"> Each use of a unary or binary operator is equivalent
to a <FONT FACE="Arial, Helvetica">function_call</FONT> with <I>function_</I><FONT FACE="Arial, Helvetica">prefix</FONT>
being the corresponding <FONT FACE="Arial, Helvetica">operator_symbol</FONT>,
and with (respectively) one or two positional actual parameters being
the operand(s) of the operator (in order). </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>2.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>To be honest: </B>We also use
the term operator (in Section 4 and in <A HREF="AA-6-1.html">6.1</A>)
to refer to one of the syntactic categories defined in <A HREF="AA-4-5.html">4.5</A>,
``<A HREF="AA-4-5.html">Operators and Expression Evaluation</A>'' whose
names end with ``_operator:'' <FONT FACE="Arial, Helvetica">logical_operator</FONT>,
<FONT FACE="Arial, Helvetica">relational_operator</FONT>, <FONT FACE="Arial, Helvetica">binary_adding_operator</FONT>,
<FONT FACE="Arial, Helvetica">unary_adding_operator</FONT>, <FONT FACE="Arial, Helvetica">multiplying_operator</FONT>,
and <FONT FACE="Arial, Helvetica">highest_precedence_operator</FONT>.
</FONT></DIV>
<H4 ALIGN=CENTER>Legality Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="Normal"> The <FONT FACE="Arial, Helvetica">subprogram_specification</FONT>
of a unary or binary operator shall have one or two parameters, respectively.
A generic function instantiation whose <FONT FACE="Arial, Helvetica">designator</FONT>
is an <FONT FACE="Arial, Helvetica">operator_symbol</FONT> is only allowed
if the specification of the generic function has the corresponding number
of parameters.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Normal"> <FONT FACE="Arial, Helvetica">Default_expression</FONT>s
are not allowed for the parameters of an operator (whether the operator
is declared with an explicit <FONT FACE="Arial, Helvetica">subprogram_specification</FONT>
or by a <FONT FACE="Arial, Helvetica">generic_instantiation</FONT>).</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Normal"> An explicit declaration of "/=" shall
not have a result type of the predefined type Boolean. </DIV>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Normal"> A declaration of "=" whose result type
is Boolean implicitly declares a declaration of "/=" that gives
the complementary result. </DIV>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>8 The operators "+"
and "-" are both unary and binary operators, and hence may
be overloaded with both one- and two-parameter functions. </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 user-defined
operators:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Examples"><TT><B>function</B> "+" (Left, Right : Matrix) <B>return</B> Matrix;<BR>
<B>function</B> "+" (Left, Right : Vector) <B>return</B> Vector;<BR>
<BR>
--<I> assuming that A, B, and C are of the type Vector</I><BR>
--<I> the following two statements are equivalent:</I><BR>
<BR>
A := B + C;<BR>
A := "+"(B, C);</TT></DIV>
<H4 ALIGN=CENTER>Extensions to Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>9.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><A NAME="I3185"></A>Explicit declarations
of "=" are now permitted for any combination of parameter and
result types.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>Explicit declarations of "/="
are now permitted, so long as the result type is not Boolean. </FONT></DIV>
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