The short answer is that "it's complicated". The most accessible long answer I'm aware of for non-C++'ers is at [1] (video). If you prefer text, the standardese

The short answer is that "it's complicated". The most accessible long answer I'm aware of for non-C++'ers is at [1] (video). If you prefer text, the standardese version is at [2]. Unfortunately I cannot find a concise text version for laymen except perhaps [3]. [1]: https://www.youtube.com/watch?v=4Xo9iH5VLQ0 https://www.youtube.com/watch?v=4Xo9iH5VLQ0 [2]: http://www.open-std.org/Jtc1/sc22/wg21/docs/papers/2014/n4047.pdf http://www.open-std.org/Jtc1/sc22/wg21/docs/papers/2014/n404... [3]: http://clang.llvm.org/docs/Modules.html http://clang.llvm.org/docs/Modules.html