On Tue, Jul 11, 2023 at 05:56:27 -0700, Jason Thorpe wrote: > > On Jul 11, 2023, at 3:17 AM, Taylor R Campbell <riastr...@netbsd.org> wrote: > > > > If we used `struct bus_dma_tag *' instead, the forward declaration > > could be `struct bus_dma_tag;' instead of having to pull in all of > > sys/bus.h, _and_ the C compiler would actually check types. > > In the original design, it's not always a struct. That was the > whole point of using a more abstract type.
The bus_dma_tag_t example from the original email is not the best one, but I didn't want to open that can of worms in my reply, so I mentioned the "not always struct" case without actually mentioning names. The style(5) specifically gives an example of a struct typedef, not of an opaque typedef. > If you want to hide the struct'ness in a machdep header file, fine, > but I completely disagree with the notion of requiring the use of > the "struct" keyword all over the place. I used to lean both ways at different times and in different contexts. I think that existence and usefulness of opaque typedefs is exactly the strong argument against using "convenience struct typedefs", b/c the latter dilute the message so to speak. If someone wants to program with "systems hungarian", they know where to find it... -uwe
