SOPE also supports "categories" to enhance a SOPE class with either new methods or new slots ("ivars" which can be navigated).

Some notes, write much more ...

As an example we use the OGo online help system, which is based on SOPE. What we want to do is to attach a new "Documentation" tree to the application which can be navigated using such an URL:


So we need to enhance the main application object (OpenGroupware class) with a "Documentation" slot which maps to the help hierarchy. Take a look at the product.plist section:

categories = {
OpenGroupware = {
slots = {
"Documentation" = {
protectedBy = "<public>";
valueClass = OGoHelpDatabase;
value = "Documentation/";

This declares a category on the "OpenGroupware" SoClass and adds a single slot "Documentation". Slots have a value class (OGoHelpDatabase) which can be initialized using a property list object (a plain string in this case).

When the SoProduct is registered and the categories are loaded the OGoHelpDatabase will be instantiated and gets send the "-initWithString:" method - the string passed is the value of the "value" key.

Note: This declares a slot on the SOPE class object, not on the application object instance! So this is also potentially executed before any object of that class is instantiated.

Thats it ;-) Now SOPE will trigger the OGoHelpDatabase object attached to the class when the "Documentation" key is triggered. The object is responsible for lookup up the subobjects as usual (in the help case this will happen dynamically based on the available help content).