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<html><head><title>Inheritance and Overloading (Programming Perl)</title><!-- STYLESHEET --><link rel="stylesheet" type="text/css" href="../style/style1.css"><!-- METADATA --><!--Dublin Core Metadata--><meta name="DC.Creator" content=""><meta name="DC.Date" content=""><meta name="DC.Format" content="text/xml" scheme="MIME"><meta name="DC.Generator" content="XSLT stylesheet, xt by James Clark"><meta name="DC.Identifier" content=""><meta name="DC.Language" content="en-US"><meta name="DC.Publisher" content="O'Reilly &amp; Associates, Inc."><meta name="DC.Source" content="" scheme="ISBN"><meta name="DC.Subject.Keyword" content=""><meta name="DC.Title" content="Inheritance and Overloading"><meta name="DC.Type" content="Text.Monograph"></head><body><!-- START OF BODY --><!-- TOP BANNER --><img src="gifs/smbanner.gif" usemap="#banner-map" border="0" alt="Book Home"><map name="banner-map"><AREA SHAPE="RECT" COORDS="0,0,466,71" HREF="index.htm" ALT="Programming Perl"><AREA SHAPE="RECT" COORDS="467,0,514,18" HREF="jobjects/fsearch.htm" ALT="Search this book"></map><!-- TOP NAV BAR --><div class="navbar"><table width="515" border="0"><tr><td align="left" valign="top" width="172"><a href="ch13_07.htm"><img src="../gifs/txtpreva.gif" alt="Previous" border="0"></a></td><td align="center" valign="top" width="171"><a href="ch13_01.htm">Chapter 13: Overloading</a></td><td align="right" valign="top" width="172"><a href="ch13_09.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0"></a></td></tr></table></div><hr width="515" align="left"><!-- SECTION BODY --><h2 class="sect1">13.8. Inheritance and Overloading</h2><p><a name="INDEX-2647"></a><a name="INDEX-2648"></a>Inheritance interacts with overloading in two ways.  The first occurswhen a handler is named as a string rather than providedas a code reference or anonymous subroutine.  When named as a string,the handler is interpreted as a method, and can therefore beinherited from superclasses.</p><p>The second interaction between inheritance and overloading is that anyclass derived from a overloaded class is itself subject to thatoverloading.  In other words, overloading is itself inherited.  Theset of handlers in a class is the union of handlers of all thatclass's ancestors, recursively.  If a handler can be found in severaldifferent ancestors, the handler actually used is governed by theusual rules for method inheritance.  For example, if class<tt class="literal">Alpha</tt> inherits from classes <tt class="literal">Beta</tt>and <tt class="literal">Gamma</tt> in that order, and class<tt class="literal">Beta</tt> overloads <tt class="literal">+</tt> with<tt class="literal">\&amp;Beta::plus_sub</tt>, but class<tt class="literal">Gamma</tt> overloads <tt class="literal">+</tt> with thestring <tt class="literal">"plus_meth"</tt>, then<tt class="literal">Beta::plus_sub</tt> will be called when you try to apply<tt class="literal">+</tt> to an <tt class="literal">Alpha</tt> object.</p><p>Since the value of the <tt class="literal">fallback</tt> key is not ahandler, its inheritance is not governed by the rules given above.  Inthe current implementation, the <tt class="literal">fallback</tt> value fromthe first overloaded ancestor is used, but this is accidental andsubject to change without notice (well, without much notice).</p><!-- BOTTOM NAV BAR --><hr width="515" align="left"><div class="navbar"><table width="515" border="0"><tr><td align="left" valign="top" width="172"><a href="ch13_07.htm"><img src="../gifs/txtpreva.gif" alt="Previous" border="0"></a></td><td align="center" valign="top" width="171"><a href="index.htm"><img src="../gifs/txthome.gif" alt="Home" border="0"></a></td><td align="right" valign="top" width="172"><a href="ch13_09.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0"></a></td></tr><tr><td align="left" valign="top" width="172">13.7. Public Overload Functions</td><td align="center" valign="top" width="171"><a href="index/index.htm"><img src="../gifs/index.gif" alt="Book Index" border="0"></a></td><td align="right" valign="top" width="172">13.9. Run-Time Overloading</td></tr></table></div><hr width="515" align="left"><!-- LIBRARY NAV BAR --><img src="../gifs/smnavbar.gif" usemap="#library-map" border="0" alt="Library Navigation Links"><p><font size="-1"><a href="copyrght.htm">Copyright &copy; 2001</a> O'Reilly &amp; Associates. All rights reserved.</font></p><map name="library-map"> <area shape="rect" coords="2,-1,79,99" href="../index.htm"><area shape="rect" coords="84,1,157,108" href="../perlnut/index.htm"><area shape="rect" coords="162,2,248,125" href="../prog/index.htm"><area shape="rect" coords="253,2,326,130" href="../advprog/index.htm"><area shape="rect" coords="332,1,407,112" href="../cookbook/index.htm"><area shape="rect" coords="414,2,523,103" href="../sysadmin/index.htm"></map><!-- END OF BODY --></body></html>
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