Self modifying has some sneaky failure modes with modern CPUs. The modification can't be too close to it's execution or it's possible to execute the old version. And it's a nightmare to debug. I have no problem with a teacher prohibiting it. That being said, it should be understood because sometimes you don't get a choice. Borland Pascal 200mhz bug, an initializer in the library would crash. You either don't use that part of the library at all, or you put something ahead of it in the initialization that will find and overwrite the bug. (The root cause was the library calibrating the number of times to spin it's wheels to get a 1 millisecond delay. CPUs above 200mhz would cause this to produce a divide underflow.)