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<html><head><title>attributes (Perl in a Nutshell, 2nd Edition)</title><link rel="stylesheet" type="text/css" href="../style/style1.css" /><meta name="DC.Creator" content="Stephen Spainhour" /><meta name="DC.Format" content="text/xml" scheme="MIME" /><meta name="DC.Language" content="en-US" /><meta name="DC.Publisher" content="O'Reilly & Associates, Inc." /><meta name="DC.Source" scheme="ISBN" content="0596002416L" /><meta name="DC.Subject.Keyword" content="stuff" /><meta name="DC.Title" content="Perl in a Nutshell, 2nd Edition" /><meta name="DC.Type" content="Text.Monograph" /></head><body bgcolor="#ffffff"><img src="gifs/smbanner.gif" usemap="#banner-map" border="0" alt="Book Home" /><map name="banner-map"><area shape="rect" coords="1,-2,616,66" href="index.htm" alt="Java and XSLT" /><area shape="rect" coords="629,-11,726,25" href="jobjects/fsearch.htm" alt="Search this book" /></map><div class="navbar"><table width="684" border="0"><tr><td align="left" valign="top" width="228"><a href="ch08_02.htm"><img src="../gifs/txtpreva.gif" alt="Previous" border="0" /></a></td><td align="center" valign="top" width="228" /><td align="right" valign="top" width="228"><a href="ch08_04.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0" /></a></td></tr></table></div><h2 class="sect1">8.3. attributes</h2><p><a name="INDEX-1273" />Replacement for<em class="emphasis">attrs.pm</em> that sets or gets the attributes ofsubroutines. Attributes are set at compile time. If an attribute isunrecognized, it will result in a fatal error. While the error istrappable, it will stop the compilation within an<tt class="literal">eval</tt>. You must be careful about naming yourattributes; an attribute that's all lowercase andnot a built-in attribute will result in a warning (unless you usewarnings "reserved"). An example of<em class="emphasis">attributes</em> is:</p><blockquote><pre class="code">sub foo : method ; use attributes ( ); # Optional, to get subroutine declarations my @attrlist = attributes::get(\&foo);</pre></blockquote><p>The built-in attributes are:</p><dl><dt><b><tt class="literal">locked</tt></b></dt><dd><a name="INDEX-1274" />Settingthis attribute is meaningful only when the subroutine or method willbe called by multiple threads. When set on a method subroutine (i.e.,one marked with the <tt class="literal">method</tt> attribute), Perlensures that any invocation of it implicitly locks its first argumentbefore execution. When set on a non-method subroutine, Perl ensuresthat a lock is taken on the subroutine itself before execution. Thesemantics of the lock are exactly those of one explicitly taken withthe "lock" operator immediatelyafter the subroutine is entered.</p></dd><dt><b><tt class="literal">method</tt></b></dt><dd><a name="INDEX-1275" />Indicates that the referencedsubroutine is a method. This has a meaning when taken together withthe <tt class="literal">locked</tt> attribute. It also means that asubroutine so marked will not trigger the "Ambiguouscall resolved as CORE::%s" warning.</p></dd><dt><b><tt class="literal">lvalue</tt></b></dt><dd><a name="INDEX-1276" />Indicatesthat the referenced subroutine is a valid lvalue and can be assignedto. The subroutine must return a modifiable value such as a scalarvariable, as described in the perlsub manpage.</p></dd></dl><p>There are no built-in attributes for anything other than subroutines.</p><hr width="684" align="left" /><div class="navbar"><table width="684" border="0"><tr><td align="left" valign="top" width="228"><a href="ch08_02.htm"><img src="../gifs/txtpreva.gif" alt="Previous" border="0" /></a></td><td align="center" valign="top" width="228"><a href="index.htm"><img src="../gifs/txthome.gif" alt="Home" border="0" /></a></td><td align="right" valign="top" width="228"><a href="ch08_04.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0" /></a></td></tr><tr><td align="left" valign="top" width="228">8.2. Attribute::Handlers</td><td align="center" valign="top" width="228"><a href="index/index.htm"><img src="../gifs/index.gif" alt="Book Index" border="0" /></a></td><td align="right" valign="top" width="228">8.4. attrs</td></tr></table></div><hr width="684" align="left" /><img src="../gifs/navbar.gif" usemap="#library-map" border="0" alt="Library Navigation Links" /><p><p><font size="-1"><a href="copyrght.htm">Copyright © 2002</a> O'Reilly & Associates. All rights reserved.</font></p><map name="library-map"><area shape="rect" coords="1,0,85,94" href="../index.htm"><area shape="rect" coords="86,1,178,103" href="../lwp/index.htm"><area shape="rect" coords="180,0,265,103" href="../lperl/index.htm"><area shape="rect" coords="267,0,353,105" href="../perlnut/index.htm"><area shape="rect" coords="354,1,446,115" href="../prog/index.htm"><area shape="rect" coords="448,0,526,132" href="../tk/index.htm"><area shape="rect" coords="528,1,615,119" href="../cookbook/index.htm"><area shape="rect" coords="617,0,690,135" href="../pxml/index.htm"></map></body></html>⌨️ 快捷键说明
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