Class-Observable module for perl

If you have ever used Java, you may have run across the java.util.Observable class
and the java.util.Observer interface. With them you can decouple an object from
the one or more objects that wish to be notified whenever particular events occur.

These events occur based on a contract with the observed item. They may occur at
the beginning, in the middle or end of a method. In addition, the object knows
that it is being observed. It just does not know how many or what types of
objects are doing the observing. It can therefore control when the messages
get sent to the obsevers.

The behavior of the observers is up to you. However, be aware that we do not do
any error handling from calls to the observers. If an observer throws a die,
it will bubble up to the observed item and require handling there. So be careful.

Throughout this documentation we refer to an 'observed item' or 'observable item'.
This ambiguity refers to the fact that both a class and an object can be observed.
The behavior when notifying observers is identical. The only difference comes in
which observers are notified.
(See "Observable Classes and Objects" for more information.)

Author: Chris Winters

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