From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 899FEE732D0 for ; Thu, 28 Sep 2023 14:22:38 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qlruA-00076z-Je; Thu, 28 Sep 2023 10:22:14 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qlru9-000766-HI for qemu-devel@nongnu.org; Thu, 28 Sep 2023 10:22:13 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qlru7-0007VO-Rs for qemu-devel@nongnu.org; Thu, 28 Sep 2023 10:22:13 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1695910931; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=1Q3sLW6wnVEf2VSwGpMREHNaKhjVIw0niZsSnVi8vZc=; b=I1Wj+KNATl+9XzNlm2DPBTsE5HsFCd4eIObKWf79ZHlALDEsFdUXvO5LgdoNVcRNHxI9hI Q7+S14CgD9XRNdKSEwf7ciA8s0wUuCjxJ27IG6t7QOr5LUmm0F7W5rp3UnWiQMsGMsO5K3 x3K+Tpe8SkYuSdsT1cwynbSxB4Lj1A8= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-150-7OA9cnNmN66z1H4QNnW5MA-1; Thu, 28 Sep 2023 10:22:09 -0400 X-MC-Unique: 7OA9cnNmN66z1H4QNnW5MA-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 0A1983816CAC for ; Thu, 28 Sep 2023 14:22:05 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.58]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C8FB3492B16; Thu, 28 Sep 2023 14:22:03 +0000 (UTC) Date: Thu, 28 Sep 2023 15:21:59 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Victor Toso Cc: qemu-devel@nongnu.org, Markus Armbruster , John Snow Subject: Re: [PATCH v1 5/9] qapi: golang: Generate qapi's union types in Go Message-ID: References: <20230927112544.85011-1-victortoso@redhat.com> <20230927112544.85011-6-victortoso@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230927112544.85011-6-victortoso@redhat.com> User-Agent: Mutt/2.2.9 (2022-11-12) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Sep 27, 2023 at 01:25:40PM +0200, Victor Toso wrote: > This patch handles QAPI union types and generates the equivalent data > structures and methods in Go to handle it. > > The QAPI union type has two types of fields: The @base and the > @Variants members. The @base fields can be considered common members > for the union while only one field maximum is set for the @Variants. > > In the QAPI specification, it defines a @discriminator field, which is > an Enum type. The purpose of the @discriminator is to identify which > @variant type is being used. > > Not that @discriminator's enum might have more values than the union's > data struct. This is fine. The union does not need to handle all cases > of the enum, but it should accept them without error. For this > specific case, we keep the @discriminator field in every union type. I still tend think the @discriminator field should not be present in the union structs. It feels like we're just trying to directly copy the C code in Go and so smells wrong from a Go POV. For most of the unions the @discriminator field will be entirely redundant, becasue the commonm case is that a @variant field exists for every possible @discriminator value. To take one example type SocketAddress struct { Type SocketAddressType `json:"type"` // Variants fields Inet *InetSocketAddress `json:"-"` Unix *UnixSocketAddress `json:"-"` Vsock *VsockSocketAddress `json:"-"` Fd *String `json:"-"` } If one was just writing Go code without the pre-existing knowledge of the QAPI C code, 'Type' is not something a Go programmer would be inclined add IMHO. And yet you are right that we need a way to represent a @discriminator value that has no corresponding @variant, since QAPI allows for that scenario. To deal with that I would suggest we just use an empty interface type. eg type SocketAddress struct { Type SocketAddressType `json:"type"` // Variants fields Inet *InetSocketAddress `json:"-"` Unix *UnixSocketAddress `json:"-"` Vsock *VsockSocketAddress `json:"-"` Fd *String `json:"-"` Fish *interface{} `json:"-"` Food *interface() `json:"-"` } the pointer value for 'Fish' and 'Food' fields here merely needs to be non-NULL, it doesn't matter what the actual thing assigned is. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|