How to point to class in external files-methods?

Good time of day to all.

In project for some classes i store some method in separate files, later special builder combine all together, but during editing in this file-method, i need to use 'self'. And it of cause doesn't see required class, because don't know which one. Can i some how in each file-method point to this class?

All method files placed under same directory, class file just on some level upper.