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)