I assume D can do incremental builds? How fast is the compile time compared to C++? Is it slower? C++ only has to read its header files and D would need to look at the entire project source code (or obj files?).
AFAIK, it is slower that compiling all at once but faster than C++ (because C++ compilation is so damn slow on its own). In D world it is most often used to avoid compiler memory limits, though, not for actual speed.
