On Sun, Feb 1, 2015 at 8:34 AM, Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> wrote: > Devin Jeanpierre wrote: > >> It's really only dynamically typed languages that have a single null >> value of a single type. Maybe I misunderstand the original statement. > > Pascal is statically typed and has a single null pointer compatible with all > pointer types. C has a single nil pointer compatible with all pointer > types. I expect that the Modula and Oberon family of languages copied > Pascal, which probably copied Algol.
No, C has a NULL macro which evaluates to something which coerces to any pointer type and will be the null value of that type. But there's one null value per type. The C standard makes no guarantees that they are compatible in any way, e.g. they can be of different sizes. On some systems, the null function pointer will have a size of N, where the null int pointer will have a size of M, where N != M -- so these are clearly not the same null value. I don't know Pascal, but I wouldn't be surprised if something similar held, as nonuniform pointer sizes were a thing once. -- Devin -- https://mail.python.org/mailman/listinfo/python-list
