This page says “All gameplay classes must be passed to the IMPLEMENT_CLASS macro in order to be implemented properly. This is done in the class source file, which is a C++ (.cpp) file that implements the class and all of its functions…”
But IMLEMENT_CLASS appears nowhere else in the documentation, nor is it used in any of the example code or starter code I searched. Specifically, I looked in the “Basic Code” template from version 4.1.0 and the “Shooter Game” example, for the same version. It’s defined in ObjectBase.h but not used anywhere.