task::weaken(3pm) [debian man page]
Task::Weaken(3pm) User Contributed Perl Documentation Task::Weaken(3pm) NAME
Task::Weaken - Ensure that a platform has weaken support DESCRIPTION
One recurring problem in modules that use Scalar::Util's "weaken" function is that it is not present in the pure-perl variant. While this isn't necesarily always a problem in a straight CPAN-based Perl environment, some operating system distributions only include the pure-Perl versions, don't include the XS version, and so weaken is then "missing" from the platform, despite passing a dependency on Scalar::Util successfully. Most notably this is RedHat Linux at time of writing, but other come and go and do the same thing, hence "recurring problem". The normal solution is to manually write tests in each distribution to ensure that "weaken" is available. This restores the functionality testing to a dependency you do once in your Makefile.PL, rather than something you have to write extra tests for each time you write a module. It should also help make the package auto-generators for the various operating systems play more nicely, because it introduces a dependency that they have to have a proper weaken in order to work. How this Task works Part of the problem seems to stem from the fact that some distributions continue to include modules even if they fail some of their tests. To get around that for this module, it will do a few dirty tricks. If Scalar::Util is not available at all, it will issue a normal dependency on the module. However, if Scalar::Util is relatively new ( it is >= 1.19 ) and the module does not have weaken, the install will bail out altogether with a long error encouraging the user to seek support from their vendor (this problem happens most often in vendor-packaged Perl versions). This distribution also contains tests to ensure that weaken is available using more normal methods. So if your module uses "weaken", you can just add the following to your Module::Install-based Makefile.PL (or equivalent). requires 'Task::Weaken' => 0; AUTHOR
Adam Kennedy <adamk@cpan.org>, <http://ali.as/> SEE ALSO
Task, Scalar::Util, <http://ali.as/> COPYRIGHT
Copyright 2006 - 2009 Adam Kennedy. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. The full text of the license can be found in the LICENSE file included with this module. perl v5.10.1 2009-06-12 Task::Weaken(3pm)
Check Out this Related Man Page
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)