Quoting Qt documentation:
The Meta-Object Compiler, moc, is the program that handles Qt's C++ extensions.
The moc tool reads a C++ header file. If it finds one or more class declarations that contain the Q_OBJECT macro, it produces a C++ source file containing the meta-object code for those classes. Among other things, meta-object code is required for the signals and slots mechanism, the run-time type information, and the dynamic property system.
The C++ source file generated by moc must be compiled and linked with the implementation of the class.
So it's kind of C++ getting turned into C++, I'm not sure if it fits in what you are looking for.