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 788CBC433F5 for ; Tue, 10 May 2022 11:45:25 +0000 (UTC) Received: from localhost ([::1]:34644 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1noOIu-0007p3-Dd for qemu-devel@archiver.kernel.org; Tue, 10 May 2022 07:45:24 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:58160) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1noOGb-00055A-HJ for qemu-devel@nongnu.org; Tue, 10 May 2022 07:43:01 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:45807) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1noOGZ-0007iY-Nt for qemu-devel@nongnu.org; Tue, 10 May 2022 07:43:01 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1652182979; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=71IKksDgzTsirAMC9E0KjxJe3YBww89inip8rySiedI=; b=bfLC4InVqCupUpNBEroERj/fyrPInchNikiuvUAQPWxX2QppDz4d8ZN5zFthAqIUosGto7 2FZOQNxqsxecKrkoC07RgqQlTDaWTHSfaBROejTUbp+VNIun3W/erHN0d4X3G+sHcoZGvy 5kMYytT2ct8fBhwM8GnOxXwhqVhwffk= Received: from mimecast-mx02.redhat.com (mx3-rdu2.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-277-lvmXHvQ6NleJpl02KW6vDA-1; Tue, 10 May 2022 07:42:57 -0400 X-MC-Unique: lvmXHvQ6NleJpl02KW6vDA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 7136C3C021A8 for ; Tue, 10 May 2022 11:42:57 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.168]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 901572024CBB; Tue, 10 May 2022 11:42:45 +0000 (UTC) Date: Tue, 10 May 2022 12:42:42 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Victor Toso Cc: qemu-devel@nongnu.org, John Snow , Eric Blake , Markus Armbruster Subject: Re: [RFC PATCH v1 4/8] qapi: golang: Generate qapi's union types in Go Message-ID: References: <20220401224104.145961-1-victortoso@redhat.com> <20220401224104.145961-5-victortoso@redhat.com> <20220510113208.ndnw7q343rz2heyo@tapioca> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220510113208.ndnw7q343rz2heyo@tapioca> User-Agent: Mutt/2.1.5 (2021-12-30) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham 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" On Tue, May 10, 2022 at 01:32:08PM +0200, Victor Toso wrote: > Hi, > > On Tue, May 10, 2022 at 11:26:56AM +0100, Daniel P. Berrangé wrote: > > On Sat, Apr 02, 2022 at 12:41:00AM +0200, Victor Toso wrote: > > > This patch handles QAPI union types and generates the equivalent data > > > structures and methods in Go to handle it. > > > > > > At the moment of this writing, it generates 67 structures. > > > > > > The QAPI union type can be summarized by its common members that are > > > defined in a @base struct and a @value. The @value type can vary and > > > depends on @base's field that we call @discriminator. The > > > @discriminator is always a Enum type. > > > > > > Golang does not have Unions. The generation of QAPI union type in Go > > > with this patch, follows similar approach to what is done for QAPI > > > struct types and QAPI alternate types. > > > > The common way to approach unions in Go is to just use a struct > > where each union case is an optional field, and declare that > > only one field must ever be set. ie > > > > type SocketAddressLegacy struct { > > // Value based on @type, possible types: > > Inet *InetSocketAddressWrapper > > Unix *UnixSocketAddressWrapper > > VSock *VsockSocketAddressWrapper > > FD *StringWrapper > > } > > Like Alternates, I like this better. > > > When deserializing from JSON we populate exactly one of the > > optional fields. > > > > When serializing to JSON process the first field that is > > non-nil. > > > > Note, you don't actually need to include the discriminator as a > > field at all, since it is implicitly determined by whichever > > case is non-nil. Introducing the discriminator as a field just > > provides the possibility for the programmer to make > > inconsistent settings, for no gain. > > Sounds reasonable. We still need to implement Marshal/Unmarshal > for unknow types (e.g: a new Type for SocketAddressLegacy was > introduced in 7.1 and we should be able to know that current > qapi-go version can't understand it). If there's a new type seen on the wire then, the easy option is to just not deserialize it at all. Return a SocketAddressLegacy struct with all fields nil, or perhaps return a full 'error', since this is likely to be significant functionalproblem for the application. 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 :|