= How this works =
This is old stuff I have rescued from my hard disk: observer pattern implemented using templates.

There are two generic classes Observer and Subject with generic implementation of the pattern.
These are implemented in Subject.h and Oberver.h files.

There are one more file test_observer.cpp where are defined two concrete implementations of Subject and Observer 
called ConcreteSubject and ConcreteObserver.

The way of use is simple. You have to derive from Subject making a template of the ConcreteSubject class and then 
call notify() when you want to say your observers that something has changed. For be able to do this you have to register
your ConcreteObserver with the subject with register_observer() method. 

ConcreteObserver class must derive from Observer and must implement its update() method
which will be called when something in ConcrteSubject changes.

For details take a look to the code.

= Compile =
$ mkdir build
$ cd build
$ cmake ..
$ make