Hi
On Fri, Aug 25, 2017 at 8:20 AM Markus Armbruster <arm...@redhat.com> wrote:
> Marc-André Lureau <marcandre.lur...@redhat.com> writes:
>
> > And misc code style fix.
> >
> > Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com>
> > ---
> > include/qapi/qmp/qlit.h | 8 ++++----
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/qapi/qmp/qlit.h b/include/qapi/qmp/qlit.h
> > index f36bca4554..1e9696988a 100644
> > --- a/include/qapi/qmp/qlit.h
> > +++ b/include/qapi/qmp/qlit.h
> > @@ -36,13 +36,13 @@ struct QLitDictEntry {
> > };
> >
> > #define QLIT_QNUM(val) \
> > - (QLitObject){.type = QTYPE_QNUM, .value.qnum = (val)}
> > + { .type = QTYPE_QNUM, .value.qnum = (val) }
> > #define QLIT_QSTR(val) \
> > - (QLitObject){.type = QTYPE_QSTRING, .value.qstr = (val)}
> > + { .type = QTYPE_QSTRING, .value.qstr = (val) }
> > #define QLIT_QDICT(val) \
> > - (QLitObject){.type = QTYPE_QDICT, .value.qdict = (val)}
> > + { .type = QTYPE_QDICT, .value.qdict = (val) }
> > #define QLIT_QLIST(val) \
> > - (QLitObject){.type = QTYPE_QLIST, .value.qlist = (val)}
> > + { .type = QTYPE_QLIST, .value.qlist = (val) }
> >
> > int compare_litqobj_to_qobj(QLitObject *lhs, QObject *rhs);
>
> Technically, this isn't a type cast, it's a compound literal. A
> compound literal is "an unnamed object whose value is given by the
> initializer list" (C99 §6.5.2.5). The standard then cautions "that this
> differs from a cast expression" (ibid).
>
You are right, but actually the patch helps with another issue if we keep
the compound type:
const QLitObject qmp_schema_qlit = QLIT_QLIST(((QLitObject[]) {
QLIT_QNULL,
{}
}));
qmp-introspect.c:17:63: error: initializer element is not constant
const QLitObject qmp_schema_qlit = QLIT_QLIST(((QLitObject[]) {
^
/home/elmarco/src/qemu/include/qapi/qmp/qlit.h:50:57: note: in definition
of macro ‘QLIT_QLIST’
(QLitObject) { .type = QTYPE_QLIST, .value.qlist = (val) }
^~~
qmp-introspect.c:17:63: note: (near initialization for ‘(anonymous).value’)
const QLitObject qmp_schema_qlit = QLIT_QLIST(((QLitObject[]) {
^
/home/elmarco/src/qemu/include/qapi/qmp/qlit.h:50:57: note: in definition
of macro ‘QLIT_QLIST’
(QLitObject) { .type = QTYPE_QLIST, .value.qlist = (val) }
^~~
Any idea how to fix that?
>
> The previous paragraph probably makes sense only to language-lawyers, so
> let's consider an example.
>
> The macro
>
> #define QLIT_QSTR(val) \
> (QLitObject){.type = QTYPE_QSTRING, .value.qstr = (val)}
>
> expands into a compound literal of type QLitObject, which can be used as
> an initializer for a variable of type QLitObject.
>
> The macro
>
> #define QLIT_QSTR(val) \
> { .type = QTYPE_QSTRING, .value.qstr = (val) }
>
> expands into something that can be used as an initializer for a variable
> of *any* structure type with suitable members. Duck typing, if you
> will.
>
> The original author's choice of compound literals is clearly
> intentional. I'd prefer to respect it unless there's a compelling
> reason not to.
>
> --
Marc-André Lureau
