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Scalar::Util(3pm)		 Perl Programmers Reference Guide		Scalar::Util(3pm)

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

	   use Scalar::Util qw(blessed dualvar isweak readonly refaddr reftype tainted weaken);

       "Scalar::Util" contains a selection of subroutines that people have expressed would be
       nice to have in the perl core, but the usage would not really be high enough to warrant
       the use of a keyword, and the size so small such that being individual extensions would be

       By default "Scalar::Util" does not export any subroutines. The subroutines defined are

       blessed EXPR
	   If EXPR evaluates to a blessed reference the name of the package that it is blessed
	   into is returned. Otherwise "undef" is returned.

	      $scalar = "foo";
	      $class  = blessed $scalar;	   # undef

	      $ref    = [];
	      $class  = blessed $ref;		   # undef

	      $obj    = bless [], "Foo";
	      $class  = blessed $obj;		   # "Foo"

       dualvar NUM, STRING
	   Returns a scalar that has the value NUM in a numeric context and the value STRING in a
	   string context.

	       $foo = dualvar 10, "Hello";
	       $num = $foo + 2; 		   # 12
	       $str = $foo . " world";		   # Hello world

       isvstring EXPR
	   If EXPR is a scalar which was coded as a vstring the result is true.

	       $vs   = v49.46.48;
	       $fmt  = isvstring($vs) ? "%vd" : "%s"; #true

       isweak EXPR
	   If EXPR is a scalar which is a weak reference the result is true.

	       $ref  = \$foo;
	       $weak = isweak($ref);		   # false
	       $weak = isweak($ref);		   # true

       openhandle FH
	   Returns FH if FH may be used as a filehandle and is open, or FH is a tied handle. Oth-
	   erwise "undef" is returned.

	       $fh = openhandle(*STDIN);	   # \*STDIN
	       $fh = openhandle(\*STDIN);	   # \*STDIN
	       $fh = openhandle(*NOTOPEN);	   # undef
	       $fh = openhandle("scalar");	   # undef

       readonly SCALAR
	   Returns true if SCALAR is readonly.

	       sub foo { readonly($_[0]) }

	       $readonly = foo($bar);		   # false
	       $readonly = foo(0);		   # true

       refaddr EXPR
	   If EXPR evaluates to a reference the internal memory address of the referenced value
	   is returned. Otherwise "undef" is returned.

	       $addr = refaddr "string";	   # undef
	       $addr = refaddr \$var;		   # eg 12345678
	       $addr = refaddr [];		   # eg 23456784

	       $obj  = bless {}, "Foo";
	       $addr = refaddr $obj;		   # eg 88123488

       reftype EXPR
	   If EXPR evaluates to a reference the type of the variable referenced is returned. Oth-
	   erwise "undef" is returned.

	       $type = reftype "string";	   # undef
	       $type = reftype \$var;		   # SCALAR
	       $type = reftype [];		   # ARRAY

	       $obj  = bless {}, "Foo";
	       $type = reftype $obj;		   # HASH

       tainted EXPR
	   Return true if the result of EXPR is tainted

	       $taint = tainted("constant");	   # false
	       $taint = tainted($ENV{PWD});	   # true if running under -T

       weaken REF
	   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.

	   This is useful for keeping copies of references , but you don't want to prevent the
	   object being DESTROY-ed at its usual time.

		 my $var;
		 $ref = \$var;
		 weaken($ref);			   # Make $ref a weak reference
	       # $ref is now undef

       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

       Copyright (c) 1997-2001 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

       Except weaken and isweak which are

       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

       The weaken and isweak subroutines in this module and the patch to the core Perl were writ-
       ten in connection  with the APress book `Tuomas J. Lukka's Definitive Guide to Object-Ori-
       ented Programming in Perl', to avoid explaining why certain things would have to be done
       in cumbersome ways.

perl v5.8.0				    2002-06-01				Scalar::Util(3pm)
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