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 refaddr reftype tainted weaken isvstring looks_like_number set_prototype); # and other useful utils appearing below
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
$vs = v49.46.48; $fmt = isvstring($vs) ? "%vd" : "%s"; #true printf($fmt,$vs);
$ref = \$foo; $weak = isweak($ref); # false weaken($ref); $weak = isweak($ref); # true
NOTE: Copying a weak reference creates a normal, strong, reference.
$copy = $ref; $weak = isweak($copy); # false
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.
$addr = refaddr "string"; # undef $addr = refaddr \$var; # eg 12345678 $addr = refaddr []; # eg 23456784
$obj = bless {}, "Foo"; $addr = refaddr $obj; # eg 88123488
undef
is returned.
$type = reftype "string"; # undef $type = reftype \$var; # SCALAR $type = reftype []; # ARRAY
$obj = bless {}, "Foo"; $type = reftype $obj; # HASH
set_prototype \&foo, '$$';
$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
Note that if you take a copy of a scalar with a weakened reference, the copy will be a strong reference.
my $var; my $foo = \$var; weaken($foo); # Make $foo a weak reference my $bar = $foo; # $bar is now a strong reference
This may be less obvious in other situations, such as grep()
, for instance
when grepping through a list of weakened references to objects that may have
been destroyed already:
@object = grep { defined } @object;
This will indeed remove all references to destroyed objects, but the remaining references to objects will be strong, causing the remaining objects to never be destroyed because there is now always a strong reference to them in the @object array.
Module use may give one of the following errors during import.
isweak
or weaken
you will need to use a newer release of perl.
isvstring
you will need to use a newer release of perl.
NAME
is only available with the XS version of Scalar::UtilScalar::Util
contains both perl and C implementations of many of its functions
so that those without access to a C compiler may still use it. However some of the functions
are only available when a C compiler was available to compile the XS version of the extension.
At present that list is: weaken, isweak, dualvar, isvstring, set_prototype
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) 1997-2007 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.
Scalar::Util - A selection of general-utility scalar subroutines |