On Wed, Jul 31, 2019 at 10:35:31AM +0200, Thomas Huth wrote: > On 30/07/2019 23.07, Eduardo Habkost wrote: > > Sometimes we use the 'struct' keyword to help us reduce > > dependencies between header files. Document that practice. > > > > Signed-off-by: Eduardo Habkost <ehabk...@redhat.com> > > --- > > I wonder if this is too terse? Should we give examples? > > --- > > HACKING | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/HACKING b/HACKING > > index 0fc3e0fc04..112685bdaf 100644 > > --- a/HACKING > > +++ b/HACKING > > @@ -101,6 +101,8 @@ it points to, or it is aliased to another pointer that > > is. > > > > 2.3. Typedefs > > Typedefs are used to eliminate the redundant 'struct' keyword. > > +However, the 'struct' keyword may be sometimes used in header > > +files to avoid unnecessary dependencies between headers. > > See also the discussion earlier this year: > > https://www.mail-archive.com/qemu-devel@nongnu.org/msg586180.html
Nice, it adds even more information than this patch. For reference, this is the patch at the URL above: -Typedefs are used to eliminate the redundant 'struct' keyword. +Typedefs can be used to eliminate the redundant 'struct' keyword. This is +especially helpful for common types that are used all over the place. Since +certain C compilers choke on duplicated typedefs, you should avoid them and +declare a typedef only in one header file. For common types, you can use +"include/qemu/typedefs.h" for example. Note that it is also perfectly fine to +use forward struct definitions without typedefs for references in headers +to avoid the problem with duplicated typedefs. I don't agree with the first two sentences, and I agree with what Paolo said here: https://www.mail-archive.com/qemu-devel@nongnu.org/msg586214.html ("I agree 100% with the wording after 'Since'. However, I think the first part should be made stronger, not weaker.") Paolo sent the following proposal: | Typedefs are use to eliminate the redundant 'struct' keyword, since type | names have a different style than other identifiers ("CamelCase" versus | "snake_case"). Each struct should have a CamelCase name and a | corresponding typedef. | | Since certain C compilers choke on duplicated typedefs, you should avoid | them and declare a typedef only in one header file. For common types, | you can use "include/qemu/typedefs.h" for example. However, as a metter | of convenience it is also perfectly fine to use forward struct | definitions instead of typedefs in headers and function prototypes; this | avoids problems with duplicated typedefs and reduces the need to include | headers from other headers. It seems perfect to me. Paolo, do I have your signed-off-by to send that in a patch? > > ... and we should merge HACKING and CODING_STYLE finally (that was on my > private TODO list, but I never found the time to do it). Agreed, but I prefer to fix one problem at a time. -- Eduardo
