One recurring problem in modules that use the Scalar::Util manpage'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 the Scalar::Util
Most notably this is RedHat Linux at time of writing, but other come and go
and do the same thing, hence "recurring problem".