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<html><head><title>Perl's Object System (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 & Associates, Inc."><meta name="DC.Source" content="" scheme="ISBN"><meta name="DC.Subject.Keyword" content=""><meta name="DC.Title" content="Perl's Object System"><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="ch12_01.htm"><img src="../gifs/txtpreva.gif" alt="Previous" border="0"></a></td><td align="center" valign="top" width="171"><a href="ch12_01.htm">Chapter 12: Objects</a></td><td align="right" valign="top" width="172"><a href="ch12_03.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">12.2. Perl's Object System</h2><p><a name="INDEX-2356"></a>Perl doesn't provide any special syntax for defining objects,classes, or methods. Instead, it reuses existing constructs toimplement these three concepts.<a href="#FOOTNOTE-1">[1]</a></p><blockquote class="footnote"><a name="FOOTNOTE-1"></a><p>[1]Now<em class="emphasis">there's</em> an example of software reuse for you!</p></blockquote><p>Here are some simple definitions that you may find reassuring:</p><dl><dt><b><em class="emphasis">An</em> <em class="emphasis">object</em> is simply a reference...er, a referent.</b></dt><dd><p><a name="INDEX-2357"></a><a name="INDEX-2358"></a>Since references let individual scalars represent larger collections ofdata, it shouldn't be a surprise that references are used for allobjects. Technically, an object isn't the reference proper--it'sreally the referent that the reference points at. This distinction isfrequently blurred by Perl programmers, however, and since we feel it'sa lovely metonymy, we will perpetuate the usage here when it suitsus.<a href="#FOOTNOTE-2">[2]</a></p><blockquote class="footnote"><a name="FOOTNOTE-2"></a><p>[2] We prefer linguistic vigor over mathematical rigor. Either you will agree or you won't.</p></blockquote></dd><dt><b><em class="emphasis">A</em> <em class="emphasis">class</em> is simply a package.</b></dt><dd><p><a name="INDEX-2359"></a>A package serves as a class by using the package's subroutines toexecute the class's methods, and by using the package's variablesto hold the class's global data. Often, a module is used to holdone or more classes.</p></dd><dt><b><em class="emphasis">A</em> <em class="emphasis">method</em> is simply a subroutine.</b></dt><dd><p><a name="INDEX-2360"></a><a name="INDEX-2361"></a>You just declare subroutines in the package you're using as theclass; these will then be used as the class's methods. Methodinvocation, a new way to call subroutines, passes an extra argument:the object or package used for invoking the method.</p></dd></dl><!-- 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="ch12_01.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="ch12_03.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0"></a></td></tr><tr><td align="left" valign="top" width="172">12.1. Brief Refresher on Object-Oriented Lingo</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">12.3. Method Invocation</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 © 2001</a> O'Reilly & 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>⌨️ 快捷键说明
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