From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43610) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dl7yw-0002e5-LA for qemu-devel@nongnu.org; Fri, 25 Aug 2017 02:20:39 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dl7yt-00009E-Em for qemu-devel@nongnu.org; Fri, 25 Aug 2017 02:20:38 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44072) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dl7yt-00008m-8q for qemu-devel@nongnu.org; Fri, 25 Aug 2017 02:20:35 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 107D35D68C for ; Fri, 25 Aug 2017 06:20:34 +0000 (UTC) From: Markus Armbruster References: <20170824103350.16400-1-marcandre.lureau@redhat.com> <20170824103350.16400-5-marcandre.lureau@redhat.com> Date: Fri, 25 Aug 2017 08:20:29 +0200 In-Reply-To: <20170824103350.16400-5-marcandre.lureau@redhat.com> (=?utf-8?Q?=22Marc-Andr=C3=A9?= Lureau"'s message of "Thu, 24 Aug 2017 12:33:40 +0200") Message-ID: <87valc2moi.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH 04/14] qlit: remove needless type cast List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau Cc: qemu-devel@nongnu.org Marc-Andr=C3=A9 Lureau writes: > And misc code style fix. > > Signed-off-by: Marc-Andr=C3=A9 Lureau > --- > 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 { > }; >=20=20 > #define QLIT_QNUM(val) \ > - (QLitObject){.type =3D QTYPE_QNUM, .value.qnum =3D (val)} > + { .type =3D QTYPE_QNUM, .value.qnum =3D (val) } > #define QLIT_QSTR(val) \ > - (QLitObject){.type =3D QTYPE_QSTRING, .value.qstr =3D (val)} > + { .type =3D QTYPE_QSTRING, .value.qstr =3D (val) } > #define QLIT_QDICT(val) \ > - (QLitObject){.type =3D QTYPE_QDICT, .value.qdict =3D (val)} > + { .type =3D QTYPE_QDICT, .value.qdict =3D (val) } > #define QLIT_QLIST(val) \ > - (QLitObject){.type =3D QTYPE_QLIST, .value.qlist =3D (val)} > + { .type =3D QTYPE_QLIST, .value.qlist =3D (val) } >=20=20 > 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 =C2=A76.5.2.5). The standard then cautions "that th= is differs from a cast expression" (ibid). The previous paragraph probably makes sense only to language-lawyers, so let's consider an example. The macro #define QLIT_QSTR(val) \ (QLitObject){.type =3D QTYPE_QSTRING, .value.qstr =3D (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 =3D QTYPE_QSTRING, .value.qstr =3D (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.