Scalar::Util - A selection of general-utility scalar subroutines

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The subroutines defined are</p> <dl> <dt id="blessed-EXPR"><a class="permalink" href="#blessed-EXPR">#</a><a id="blessed"></a>blessed EXPR</dt> <dd> <p>If EXPR evaluates to a blessed reference the name of the package that it is blessed into is returned. Otherwise <code>undef</code> is returned.</p> <pre><code>$scalar = "foo"; $class = blessed $scalar; # undef $ref = []; $class = blessed $ref; # undef $obj = bless [], "Foo"; $class = blessed $obj; # "Foo"</code></pre> </dd> <dt id="dualvar-NUM,-STRING"><a class="permalink" href="#dualvar-NUM,-STRING">#</a><a id="dualvar"></a><a id="dualvar-NUM-STRING"></a>dualvar NUM, STRING</dt> <dd> <p>Returns a scalar that has the value NUM in a numeric context and the value STRING in a string context.</p> <pre><code>$foo = dualvar 10, "Hello"; $num = $foo + 2; # 12 $str = $foo . " world"; # Hello world</code></pre> </dd> <dt id="isvstring-EXPR"><a class="permalink" href="#isvstring-EXPR">#</a><a id="isvstring"></a>isvstring EXPR</dt> <dd> <p>If EXPR is a scalar which was coded as a vstring the result is true.</p> <pre><code>$vs = v49.46.48; $fmt = isvstring($vs) ? "%vd" : "%s"; #true printf($fmt,$vs);</code></pre> </dd> <dt id="isweak-EXPR"><a class="permalink" href="#isweak-EXPR">#</a><a id="isweak"></a>isweak EXPR</dt> <dd> <p>If EXPR is a scalar which is a weak reference the result is true.</p> <pre><code>$ref = \$foo; $weak = isweak($ref); # false weaken($ref); $weak = isweak($ref); # true</code></pre> </dd> <dt id="looks_like_number-EXPR"><a class="permalink" href="#looks_like_number-EXPR">#</a><a id="looks_like_number"></a>looks_like_number EXPR</dt> <dd> <p>Returns true if perl thinks EXPR is a number. See <a href="/5.8.5/perlapi#looks_like_number">"looks_like_number" in perlapi</a>.</p> </dd> <dt id="openhandle-FH"><a class="permalink" href="#openhandle-FH">#</a><a id="openhandle"></a>openhandle FH</dt> <dd> <p>Returns FH if FH may be used as a filehandle and is open, or FH is a tied handle. Otherwise <code>undef</code> is returned.</p> <pre><code>$fh = openhandle(*STDIN); # \*STDIN $fh = openhandle(\*STDIN); # \*STDIN $fh = openhandle(*NOTOPEN); # undef $fh = openhandle("scalar"); # undef</code></pre> </dd> <dt id="readonly-SCALAR"><a class="permalink" href="#readonly-SCALAR">#</a><a id="readonly"></a>readonly SCALAR</dt> <dd> <p>Returns true if SCALAR is readonly.</p> <pre><code>sub foo { readonly($_[0]) } $readonly = foo($bar); # false $readonly = foo(0); # true</code></pre> </dd> <dt id="refaddr-EXPR"><a class="permalink" href="#refaddr-EXPR">#</a><a id="refaddr"></a>refaddr EXPR</dt> <dd> <p>If EXPR evaluates to a reference the internal memory address of the referenced value is returned. Otherwise <code>undef</code> is returned.</p> <pre><code>$addr = refaddr "string"; # undef $addr = refaddr \$var; # eg 12345678 $addr = refaddr []; # eg 23456784 $obj = bless {}, "Foo"; $addr = refaddr $obj; # eg 88123488</code></pre> </dd> <dt id="reftype-EXPR"><a class="permalink" href="#reftype-EXPR">#</a><a id="reftype"></a>reftype EXPR</dt> <dd> <p>If EXPR evaluates to a reference the type of the variable referenced is returned. Otherwise <code>undef</code> is returned.</p> <pre><code>$type = reftype "string"; # undef $type = reftype \$var; # SCALAR $type = reftype []; # ARRAY $obj = bless {}, "Foo"; $type = reftype $obj; # HASH</code></pre> </dd> <dt id="set_prototype-CODEREF,-PROTOTYPE"><a class="permalink" href="#set_prototype-CODEREF,-PROTOTYPE">#</a><a id="set_prototype"></a><a id="set_prototype-CODEREF-PROTOTYPE"></a>set_prototype CODEREF, PROTOTYPE</dt> <dd> <p>Sets the prototype of the given function, or deletes it if PROTOTYPE is undef. Returns the CODEREF.</p> <pre><code>set_prototype \&foo, '$$';</code></pre> </dd> <dt id="tainted-EXPR"><a class="permalink" href="#tainted-EXPR">#</a><a id="tainted"></a>tainted EXPR</dt> <dd> <p>Return true if the result of EXPR is tainted</p> <pre><code>$taint = tainted("constant"); # false $taint = tainted($ENV{PWD}); # true if running under -T</code></pre> </dd> <dt id="weaken-REF"><a class="permalink" href="#weaken-REF">#</a><a id="weaken"></a>weaken REF</dt> <dd> <p>REF will be turned into a weak reference. This means that it will not hold a reference count on the object it references. Also when the reference count on that object reaches zero, REF will be set to undef.</p> <p>This is useful for keeping copies of references , but you don't want to prevent the object being DESTROY-ed at its usual time.</p> <pre><code>{ my $var; $ref = \$var; weaken($ref); # Make $ref a weak reference } # $ref is now undef</code></pre> </dd> </dl> <h1 id="KNOWN-BUGS"><a class="permalink" href="#KNOWN-BUGS">#</a><a id="KNOWN"></a>KNOWN BUGS</h1> <p>There is a bug in perl5.6.0 with UV's that are >= 1<<31. This will show up as tests 8 and 9 of dualvar.t failing</p> <h1 id="COPYRIGHT"><a class="permalink" href="#COPYRIGHT">#</a>COPYRIGHT</h1> <p>Copyright (c) 1997-2004 Graham Barr <gbarr@pobox.com>. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.</p> <p>Except weaken and isweak which are</p> <p>Copyright (c) 1999 Tuomas J. Lukka <lukka@iki.fi>. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as perl itself.</p> <h1 id="BLATANT-PLUG"><a class="permalink" href="#BLATANT-PLUG">#</a><a id="BLATANT"></a>BLATANT PLUG</h1> <p>The weaken and isweak subroutines in this module and the patch to the core Perl were written in connection with the APress book `Tuomas J. Lukka's Definitive Guide to Object-Oriented Programming in Perl', to avoid explaining why certain things would have to be done in cumbersome ways.</p> </div> <div id="footer"> <p>Perldoc Browser is maintained by Dan Book (<a href="https://metacpan.org/author/DBOOK">DBOOK</a>). Please contact him via the <a href="https://github.com/Grinnz/perldoc-browser/issues">GitHub issue tracker</a> or <a href="mailto:dbook@cpan.org">email</a> regarding any issues with the site itself, search, or rendering of documentation.</p> <p>The Perl documentation is maintained by the Perl 5 Porters in the development of Perl. 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Scalar::Util - A selection of general-utility scalar subroutines - Perldoc Browser