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 53EA4C433F5 for ; Tue, 10 May 2022 11:30:52 +0000 (UTC) Received: from localhost ([::1]:44342 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1noO4p-0003Jy-6S for qemu-devel@archiver.kernel.org; Tue, 10 May 2022 07:30:51 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:55264) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1noO2x-0000yE-4R for qemu-devel@nongnu.org; Tue, 10 May 2022 07:28:56 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:39180) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1noO2s-0005TI-KA for qemu-devel@nongnu.org; Tue, 10 May 2022 07:28:52 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1652182129; 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=YjsxZ6yl2Vub92c5GxSuujBhzFID676aDf3FoGmdjd4=; b=Wf7mn326fdh1b0u1n39JuZXTSaWHZlKCuRaliHSBYVyYy42SEtoqXGFA3rDUzomcfknckr KP8Bl6Ok2LWusaPovjF8RPP0KiiSZbFpY3ye/SJ5uOUa2pmbHq+Wn+AYlw6JJUYLg7HAzv HalBIjig8FDg2F04taQ8U2d4OTkMZjs= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-484-EPh4MDzJOfeJXy9cu3QjNA-1; Tue, 10 May 2022 07:28:48 -0400 X-MC-Unique: EPh4MDzJOfeJXy9cu3QjNA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 3AC9C1011637 for ; Tue, 10 May 2022 11:28:48 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.168]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 58AE0111E407; Tue, 10 May 2022 11:28:43 +0000 (UTC) Date: Tue, 10 May 2022 12:28:40 +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 2/8] qapi: golang: Generate qapi's alternate types in Go Message-ID: References: <20220401224104.145961-1-victortoso@redhat.com> <20220401224104.145961-3-victortoso@redhat.com> <20220510112129.befwqkqtkdhyah5h@tapioca> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220510112129.befwqkqtkdhyah5h@tapioca> User-Agent: Mutt/2.1.5 (2021-12-30) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 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: -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 01:21:29PM +0200, Victor Toso wrote: > Hi, > > On Tue, May 10, 2022 at 11:10:45AM +0100, Daniel P. Berrangé wrote: > > On Sat, Apr 02, 2022 at 12:40:58AM +0200, Victor Toso wrote: > > > This patch handles QAPI alternate types and generates data > > > structures in Go that handles it. > > > > > > At this moment, there are 5 alternates in qemu/qapi, they are: > > > * BlockDirtyBitmapMergeSource > > > * Qcow2OverlapChecks > > > * BlockdevRef > > > * BlockdevRefOrNull > > > * StrOrNull > > > > > > Alternate types are similar to Union but without a > > > discriminator that can be used to identify the underlying > > > value on the wire. It is needed to infer it. That can't be > > > easily mapped in Go. > > > > I don't buy that. Given this example: > > > > type BlockdevRef struct { > > // Options are: > > // * definition (BlockdevOptions): defines a new block device inline > > // * reference (string): references the ID of an existing block device > > Value Any > > } > > > > What is the problem with having this Go struct: > > > > type BlockdevRef struct { > > Definition *BlockdevOptions > > Reference *string > > } > > ... this is better. > > > when deserializing from JSON, we know exactly which one of > > these two fields to populate. The programmer consuming this can > > look at which field is non-nil. > > > > When serializing to JSON, we serialize which ever field is > > non-nil. > > > > If both fields are non-nil that's a programmer bug. Either > > ignore it and only serialize the first non-nil field, or raise > > an error. > > It would be a programmer bug if they set a Value of a type not > allowed by Type's spec, but it would be a *runtime* error. Your > suggestion is more type safe. Yep, essentially I'm saying I want the code to enable type checking to be done at compile time instead of runtime, whenever it is possible to achieve that from a technical POV. 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 :|