PPT-Folie
Data::Locations are typeglobs, filehandles and objects
at the same time
The typeglob is blessed into the Data::Locations class
The filehandle is tied to the object (i.e., to itself,
because Perl confuses typeglobs and filehandles)
The typeglob's slots ($, @, %) contain the object's data
(the "@" slot actually contains the user's data)
Symbolic references are used as "weak references"
for internal interconnections
The reference count is adjusted so that the Location will
be destroyed when user's last reference goes out of scope
The symbol table %Data::Locations:: is used as index
(for "weak reference" lookups and global destruction)