| Scalar::Util - A selection of general-utility scalar subroutines |
Scalar::Util - A selection of general-utility scalar subroutines
use Scalar::Util qw(blessed dualvar isweak readonly 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 wasteful.
By default Scalar::Util does not export any subroutines. The
subroutines defined are
undef is returned.
$scalar = "foo"; $class = blessed $scalar; # undef
$ref = []; $class = blessed $ref; # undef
$obj = bless [], "Foo"; $class = blessed $obj; # "Foo"
$foo = dualvar 10, "Hello";
$num = $foo + 2; # 12
$str = $foo . " world"; # Hello world
$ref = \$foo;
$weak = isweak($ref); # false
weaken($ref);
$weak = isweak($ref); # true
undef is returned.
$fh = openhandle(*STDIN); # \*STDIN
$fh = openhandle(\*STDIN); # \*STDIN
$fh = openhandle(*NOTOPEN); # undef
$fh = openhandle("scalar"); # undef
=item readonly SCALAR
Returns true if SCALAR is readonly.
sub foo { readonly($_[0]) }
$readonly = foo($bar); # false
$readonly = foo(0); # true
undef is returned.
$type = reftype "string"; # undef
$type = reftype \$var; # SCALAR
$type = reftype []; # ARRAY
$obj = bless {}, "Foo";
$type = reftype $obj; # HASH
$taint = tainted("constant"); # false
$taint = tainted($ENV{PWD}); # true if running under -T
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 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 modify it under the same terms as perl itself.
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.
| Scalar::Util - A selection of general-utility scalar subroutines |