This is Perl module Scalar::Util::Instance.

INSTALLATION

Scalar::Util::Instance installation is straightforward. If your CPAN shell is set up, you should just be able to do

$ cpan Scalar::Util::Instance

Download it, unpack it, then build it as per the usual:

$ perl Makefile.PL
$ make && make test

Then install it:

$ make install

DOCUMENTATION

Scalar::Util::Instance documentation is available as in POD. So you can do:

$ perldoc Scalar::Util::Instance

to read the documentation online with your favorite pager.

Goro Fuji (gfx)