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<html><head><title>Comma Operators (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="Comma Operators"><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="ch03_17.htm"><img src="../gifs/txtpreva.gif" alt="Previous" border="0"></a></td><td align="center" valign="top" width="171"><a href="ch03_01.htm">Chapter 3: Unary and Binary Operators</a></td><td align="right" valign="top" width="172"><a href="ch03_19.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">3.18. Comma Operators</h2><p><a name="INDEX-1011"></a><a name="INDEX-1012"></a><a name="INDEX-1013"></a><a name="INDEX-1014"></a>Binary "<tt class="literal">,</tt>" is the comma operator.  In scalar context it evaluatesits left argument in void context, throws that value away, then evaluates its rightargument in scalar context and returns that value.  This is just like C's comma operator.For example:<blockquote><pre class="programlisting">$a = (1, 3);</pre></blockquote>assigns <tt class="literal">3</tt> to <tt class="literal">$a</tt>.  Do not confuse the scalar context use with thelist context use.  In list context, a comma is just the list argumentseparator, and inserts both its arguments into the <em class="replaceable">LIST</em>.  It doesnot throw any values away.</p><p>For example, if you change the previous example to:<blockquote><pre class="programlisting">@a = (1, 3);</pre></blockquote>you are constructing a two-element list, while:<blockquote><pre class="programlisting">atan2(1, 3);</pre></blockquote>is calling the function <tt class="literal">atan2</tt> with two arguments.</p><p><a name="INDEX-1015"></a>The <tt class="literal">=&gt;</tt> digraph is mostly just a synonym for the comma operator.It's useful for documenting arguments that come in pairs.  It alsoforces any identifier to its immediate left to be interpreted as a string.</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="ch03_17.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="ch03_19.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0"></a></td></tr><tr><td align="left" valign="top" width="172">3.17. Assignment Operators</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">3.19. List Operators (Rightward)</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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