[{"id":13465,"web_url":"https://patchwork.libcamera.org/comment/13465/","msgid":"<20201024163312.7e4yc6nmwvznvwbw@uno.localdomain>","date":"2020-10-24T16:33:12","subject":"Re: [libcamera-devel] [PATCH] libcamera: controls: Disable\n\tControlValue construction from unsupported T","submitter":{"id":3,"url":"https://patchwork.libcamera.org/api/people/3/","name":"Jacopo Mondi","email":"jacopo@jmondi.org"},"content":"Hi Laurent,\n\nOn Sat, Oct 24, 2020 at 01:00:20AM +0300, Laurent Pinchart wrote:\n> The ControlValue constructor for non-array values is a template\n> function that participates in overload resolution for all T types that\n> are not Span or std::string. Other T types that are not supported then\n> result in a compilation error.\n>\n> This causes issues when calling an overloaded function that can accept\n> both a ControlValue and a Span with an std::array parameter. The\n> first overload will be resolved using implicit construction of a\n> ControlValue from the std::array, while the second overload will be\n> resolved using implicit construction of a Span from the\n> std::array. This results in a compilation error due to an ambiguous\n> function call.\n>\n> The first overload is invalid, selecting it would result in a\n> compilation error in the ControlValue constructor, as the\n> ControlValue constructor doesn't support std::array for type T.\n> The compiler can't know about that, as overload resolution happens\n> earlier.\n\nmind->bend();\n\n:)\n\n>\n> To fix it, we can disable the ControlValue constructor for\n> unsupported types T, moving the type check from compilation of the\n> function to overload resolution. The constructor will not participate in\n> overload resolution, and the call won't be ambiguous. The end result is\n> the same for unsupported types, compilation will fail.\n>\n> Signed-off-by: Laurent Pinchart \n\nThanks, this should solve the issue I had with ControlInfo()\nconstructor that took a Span\n\nReviewed-by: Jacopo Mondi \n\nThanks\n j\n\n> ---\n> include/libcamera/controls.h | 1 +\n> 1 file changed, 1 insertion(+)\n>\n> diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h\n> index 3d7f4b0dc1a7..3b7f3347761e 100644\n> --- a/include/libcamera/controls.h\n> +++ b/include/libcamera/controls.h\n> @@ -97,6 +97,7 @@ public:\n>\n> #ifndef __DOXYGEN__\n> \ttemplate::value &&\n> +\t\t\t\t\t\t details::control_type::value &&\n> \t\t\t\t\t\t !std::is_same>::value,\n> \t\t\t\t\t\t std::nullptr_t> = nullptr>\n> \tControlValue(const T &value)\n> --\n> Regards,\n>\n> Laurent Pinchart\n>","headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id 038EFC3B5C\n\tfor ;\n\tSat, 24 Oct 2020 16:33:16 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 77BE661D64;\n\tSat, 24 Oct 2020 18:33:15 +0200 (CEST)","from relay3-d.mail.gandi.net (relay3-d.mail.gandi.net\n\t[217.70.183.195])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id A786C605BF\n\tfor ;\n\tSat, 24 Oct 2020 18:33:14 +0200 (CEST)","from uno.localdomain (2-224-242-101.ip172.fastwebnet.it\n\t[2.224.242.101]) (Authenticated sender: jacopo@jmondi.org)\n\tby relay3-d.mail.gandi.net (Postfix) with ESMTPSA id 0887F60004;\n\tSat, 24 Oct 2020 16:33:13 +0000 (UTC)"],"X-Originating-IP":"2.224.242.101","Date":"Sat, 24 Oct 2020 18:33:12 +0200","From":"Jacopo Mondi ","To":"Laurent Pinchart ","Message-ID":"<20201024163312.7e4yc6nmwvznvwbw@uno.localdomain>","References":"<20201023220020.22536-1-laurent.pinchart@ideasonboard.com>","MIME-Version":"1.0","Content-Disposition":"inline","In-Reply-To":"<20201023220020.22536-1-laurent.pinchart@ideasonboard.com>","Subject":"Re: [libcamera-devel] [PATCH] libcamera: controls: Disable\n\tControlValue construction from unsupported T","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Cc":"libcamera-devel@lists.libcamera.org","Content-Type":"text/plain; charset=\"us-ascii\"","Content-Transfer-Encoding":"7bit","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}}]