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Message: <blockquote data-quote="Archimedes" data-source="post: 342480" data-attributes="member: 5281">I’d be happy to.I don’t know what languages you’re familiar with, so I’ll keep it general.Start with two classes named something like Observer and Observed.Give the Observer class a method that’s traditionally named Update.  Pass a reference to an Observed as an argument since the Observer may be watching more than one Observed and it’ll need to get at the data anyway.Give the Observed class a list with type Observer and two methods, Add & Delete, that accept a reference to Observer as arguments.  These methods add and remove the given Observers from the list.  Most importantly give the Observed a method that’s traditionally named Notify.  This method loops through the Observer list calling Update on each Observer reference.These classes are usually used as Mix-Ins in languages that support multiple inheritance.  In something like Java you can use Interfaces or Delegation.  In the class that inherits from Observer you’ll want to override the Update method according to purpose and use the Observed’s Add method to register with said Observed.  The later is often done in the Observer’s constructor.In the class that inherits from Observed you’ll want to add the Notify method to the end of whatever method is used to modify the Observed.Setting up this pattern is trivial in languages like Python, Ruby, or even LISP(Someone did mention Paul Graham).  It’s also fairly simple in C++, but a little harder than it needs to be in Java.You can make your objects both Observer and Observed, with the Observer notifying it’s own Observers when updated.  That’s how you can avoid writing those logic tables of cascades yourself.You can get fancier with the Observer if you want, using different Notify method that call variant Update methods or even using a vector instead of a list and registering a callback to replace Update when calling the Add method.Maybe that’s enough for you to start looking.  You should be able to find examples written in your language of choice out there somewhere. <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f642.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":)" title="Smile    :)"  data-smilie="1"data-shortname=":)" />Sam</blockquote>

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