It does not break anything. Just uses C++ and builds upon it and improves it. And MOC comes in when some niceties are required that are hard to do with plain C++ (and be backwards compatible) or when more flexibility is required. If you know how to do it better, well Qt is free (as in freedom) and opensource and you can join the project and replace MOC with a better implementation. Until then it is a not so important detail and foolish to throw away entire Qt and all the numerous goodies and nice things that it brings just for this small detail.