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Manual Reference Pages  -  TASK::WEAKEN (3)

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Task::Weaken - Ensure that a platform has weaken support



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, <B>despiteB> 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 <B>haveB> 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 <B>notB> 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;


Bugs should be always be reported via the CPAN bug tracker at


For other issues,contact the author.


Adam Kennedy <>


Task, Scalar::Util, <>


Copyright 2006 - 2011 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.

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perl v5.20.3 TASK::WEAKEN (3) 2011-03-08

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