While the perldoc/tie manpage allows tying to an arbitrary object, the
class in question must support this in it's implementation of 'TIEHASH',
'TIEARRAY' or whatever.
This class provides a very tie constructor that simply returns the object
it was given as it's first argument.
This way side effects of calling '$object->TIEHASH' are avoided.
This is used in the Data::Visitor manpage in order to tie a variable to an
already existing object. This is also useful for cloning, when you want to
clone the internal state object instead of going through the tie interface
for that variable.