C modules

Apple innovates: http://llvm.org/devmtg/2012-11/Gregor-Modules.pdf

>>16
Even with include guards you still need to open and parse the header every time it's #included - you can just do it a bit quicker. And if you've ever tried to integrate large code bases from different sources you know those are unfortunately not bad examples. (Windows system headers seem to work especially hard to cause collisions)