There is a coding pattern that has been proliferating the X++ code base for years. It is not an X++ best practices – nor is it object oriented; yet it is used quite heavily (unfortunately). Consider a simple class hierarchy with an abstract base class and 3 derived classes. A typical implementation of a factory would be a static method on the base class, like this: (Please ignore the type of the parameter – it could be anything, I choose str for simplicity)
Now; the problems with this approach are many.
The coupling between the 4 classes spells trouble. If you try to modularize an application written like this, you will quickly realize that the pattern above is bad. You cannot have references from lower-level models (aka. assemblies/modules) to higher-level models. Yet; having a single factory method is valuable and a good practice.
SysExtension Framework to the rescue.
Consider you decorate the subclasses with an attribute, like depicted here:
Then you can rewrite the factory method to this:
The extension framework returns an instance of the right subclass automatically. It uses the attribute to determine which subclass instance to create. Quite simple – extraordinary powerful!
A few words of caution: There is a small performance impact on cold systems when using the SysExtension framework. In most cases you will not notice it; however – for performance critical paths, you should measure the impact of this change before going for it.
To learn more about the SysExtension framework see here.