This is Perl module WeakRef::Auto.
INSTALLATION
WeakRef::Auto installation is straightforward. If your CPAN shell is set up,
you should just be able to do
$ cpan WeakRef::Auto
Download it, unpack it, then build it as per the usual:
$ perl Makefile.PL
$ make && make test
Then install it:
$ make install
DOCUMENTATION
WeakRef::Auto documentation is available as in POD. So you can do:
$ perldoc WeakRef::Auto
to read the documentation online with your favorite pager.
Goro Fuji