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

NAME

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

SYNOPSIS

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

DESCRIPTION

       "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 wasteful.

       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
	       printf($fmt,$vs);

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

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

       openhandle FH
	   Returns FH if FH may be used as a filehandle and is open, or FH is a tied handle. Otherwise "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. Otherwise "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

KNOWN BUGS

       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

       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 itself.

       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 mod-
       ify it under the same terms as perl itself.

BLATANT PLUG

       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 cumber-
       some ways.

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