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Tue, 24 Nov 2020 16:20:37 +0100 (CET) From: Markus Armbruster To: Eduardo Habkost Subject: Re: [PATCH v2 3/8] qnum: QNumValue type for QNum value literals References: <20201117144246.GD1235237@habkost.net> <87mtzdd4p7.fsf@dusky.pond.sub.org> <20201119182158.GX1509407@habkost.net> <877dqg8ukz.fsf@dusky.pond.sub.org> <20201120182720.GF2271382@habkost.net> <877dqcwlxc.fsf@dusky.pond.sub.org> <20201123183357.GK2271382@habkost.net> <87ft4zp2at.fsf@dusky.pond.sub.org> <20201124144102.GL2271382@habkost.net> Date: Tue, 24 Nov 2020 16:20:37 +0100 In-Reply-To: <20201124144102.GL2271382@habkost.net> (Eduardo Habkost's message of "Tue, 24 Nov 2020 09:41:02 -0500") Message-ID: <877dqahjcq.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Received-SPF: pass client-ip=63.128.21.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , "Daniel P. =?utf-8?Q?Berrang=C3=A9?=" , QEMU Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Eduardo Habkost writes: > On Tue, Nov 24, 2020 at 09:49:30AM +0100, Markus Armbruster wrote: >> Eduardo Habkost writes: >> >> > On Mon, Nov 23, 2020 at 08:51:27AM +0100, Markus Armbruster wrote: >> >> Eduardo Habkost writes: >> >> >> >> > On Fri, Nov 20, 2020 at 06:29:16AM +0100, Markus Armbruster wrote: >> >> [...] >> >> >> When the structure of a data type is to be kept away from its users, I >> >> >> prefer to keep it out of the public header, so the compiler enforces the >> >> >> encapsulation. >> >> > >> >> > I prefer that too, except that it is impossible when users of the >> >> > API need the compiler to know the struct size. >> >> >> >> There are cases where the structure of a data type should be >> >> encapsulated, yet its size must be made known for performance (avoid >> >> dynamic memory allocation and pointer chasing). >> >> >> >> Need for encapsulation correlates with complex algorithms and data >> >> structures. The cost of dynamic allocation is often in the noise then. >> > >> > I don't know what we are talking about anymore. None of this >> > applies to the QNum API, right? >> > >> > QNum/QNumValue are not complex data structures, and the reason we >> > need the compiler to know the size of QNumValue is not related to >> > performance at all. >> >> We started with the question whether to make QNumValue's members >> private. We digressed to the question when to make members private. >> So back to the original question. >> >> > We might still want to discourage users of the QNum API from >> > accessing QNum.u/QNumValue.u directly. Documenting the field as >> > private is a very easy way to do it. >> >> It's a complete non-issue. QNum has been around for years, and we >> haven't had any issues that could've been plausibly avoided by asking >> people to refrain from accessing its members. >> >> If there was an actual need to keep the members private, I'd move the >> struct out of the header, so the compiler enforces privacy. > > Understood. There's still a question I'd like to answer, to > decide how the API documentation should look like: > > Is QNum.u/QNumValue.u required to be part of the API > documentation? > > If accessing that field directly is not necessary for using the > API, I don't think it should appear in the documentation (because > it would be just noise). The current patch's comment on QNumValue looks good to me. Does this answer your question?