Afshin:
Can someone explain how to organize a set of classes into a module (or namespace, or package) so that each class can have their own file?
Lot of D code is not made of classes :-) There are also lot of free functions, some templates, some type definitions, some interfaces, some global constants or variables, module constructors, and more.
Often don't put a single class in each module. Generally you put related stuff in a single module.
Bye, bearophile