[{"id":22579,"web_url":"https://patchwork.libcamera.org/comment/22579/","msgid":"","date":"2022-04-05T16:27:20","subject":"Re: [libcamera-devel] [PATCH v2 3/5] provide a default fixed-sized\n\tSpan constructor","submitter":{"id":2,"url":"https://patchwork.libcamera.org/api/people/2/","name":"Laurent Pinchart","email":"laurent.pinchart@ideasonboard.com"},"content":"Hi Christian,\n\nThank you for the patch.\n\nOn Tue, Apr 05, 2022 at 01:42:13AM +0100, Christian Rauch via libcamera-devel wrote:\n> This allows to construct empty 0-fixed-sized Spans.\n> \n> Signed-off-by: Christian Rauch \n> ---\n> include/libcamera/base/span.h | 2 --\n> include/libcamera/controls.h | 2 +-\n> 2 files changed, 1 insertion(+), 3 deletions(-)\n> \n> diff --git a/include/libcamera/base/span.h b/include/libcamera/base/span.h\n> index 88d2e3de..bff4c115 100644\n> --- a/include/libcamera/base/span.h\n> +++ b/include/libcamera/base/span.h\n> @@ -105,8 +105,6 @@ public:\n> \n> \tstatic constexpr std::size_t extent = Extent;\n> \n> -\ttemplate -\t\t typename = std::enable_if_t>\n\nThe issue here is that the std::span class has this constraint ([1]):\n\n This overload participates in overload resolution only if\n extent == 0 || extent == std::dynamic_extent.\n\n[1] https://en.cppreference.com/w/cpp/container/span/span\n\nIf we drop the constraint here, we will have an issue when switching to\nstd::span in the future. Is there a way we could achieve the result\nyou're aiming for without this change ?\n\n> \tconstexpr Span() noexcept\n> \t\t: data_(nullptr)\n> \t{\n> diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h\n> index 665bcac1..de8a7770 100644\n> --- a/include/libcamera/controls.h\n> +++ b/include/libcamera/controls.h\n> @@ -167,7 +167,7 @@ public:\n> \n> \t\tusing V = typename T::value_type;\n> \t\tconst V *value = reinterpret_cast(data().data());\n> -\t\treturn { value, numElements_ };\n> +\t\treturn T{ value, numElements_ };\n> \t}\n> \n> #ifndef __DOXYGEN__","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 59D40C0F1B\n\tfor ;\n\tTue, 5 Apr 2022 16:27:26 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id B281265642;\n\tTue, 5 Apr 2022 18:27:25 +0200 (CEST)","from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 36278604BB\n\tfor ;\n\tTue, 5 Apr 2022 18:27:24 +0200 (CEST)","from pendragon.ideasonboard.com\n\t(117.145-247-81.adsl-dyn.isp.belgacom.be [81.247.145.117])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id AA00E5D;\n\tTue, 5 Apr 2022 18:27:23 +0200 (CEST)"],"DKIM-Signature":["v=1; a=rsa-sha256; c=relaxed/simple; d=libcamera.org;\n\ts=mail; t=1649176045;\n\tbh=ER0cbFMKUa7ivStO2B3JnQXjQhitCjlVZP/KBtG8xGY=;\n\th=Date:To:References:In-Reply-To:Subject:List-Id:List-Unsubscribe:\n\tList-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc:\n\tFrom;\n\tb=qWBk6WprZxXjFOM2iHO0psKYvrLowZLuDalcVasm78PP67QoGxw9Q58Qo7PZCpruA\n\ty/Vt7YEfYROqA2koDQpFA08wOF+riUSTHUMU+DSjCVIsJ3IcEhHucGLXNWNHqygzb8\n\tzAOCBihA9PrbpzK/3ml5LdZyx5GMWcwLnfIh66o9T1Hdi2lpN1AddZ9Cbj1ELcPh5T\n\tU1w8PwW5btJ7xnB90/l5Gf5Gp1pyDHvbVhcw6Ud7m5c0GDfcIoY6vY9FOzio8vbQdH\n\tTl0a+1zmxz97U+Kwlwped33R8A0nXxbArg7NxJ2/VEIe1du4l4l9GQDG3QbuR9xhsq\n\tumhG5OT4NEpdA==","v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1649176043;\n\tbh=ER0cbFMKUa7ivStO2B3JnQXjQhitCjlVZP/KBtG8xGY=;\n\th=Date:From:To:Cc:Subject:References:In-Reply-To:From;\n\tb=k3YbpZ/+iXUho5X8HmCJC6NMl9YNWA86PpzB8dhyha7u9GK9i5Jn+jhCNj+lWYoAs\n\t1Tl2Hq6ggWEzP0+ftDQgUrVQNjqvzFL+jB89B8EtViZKUC7pI4qq7kBgpsKjmuNr9w\n\tItEyg9NRgWgK/KI6OFhW74mHWh3tL63ILy9qUjfM="],"Authentication-Results":"lancelot.ideasonboard.com; dkim=pass (1024-bit key; \n\tunprotected) header.d=ideasonboard.com\n\theader.i=@ideasonboard.com\n\theader.b=\"k3YbpZ/+\"; dkim-atps=neutral","Date":"Tue, 5 Apr 2022 19:27:20 +0300","To":"Christian Rauch ","Message-ID":"","References":"<20220405004215.86340-1-Rauch.Christian@gmx.de>\n\t<20220405004215.86340-4-Rauch.Christian@gmx.de>","MIME-Version":"1.0","Content-Type":"text/plain; charset=utf-8","Content-Disposition":"inline","In-Reply-To":"<20220405004215.86340-4-Rauch.Christian@gmx.de>","Subject":"Re: [libcamera-devel] [PATCH v2 3/5] provide a default fixed-sized\n\tSpan constructor","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","From":"Laurent Pinchart via libcamera-devel\n\t","Reply-To":"Laurent Pinchart ","Cc":"libcamera-devel@lists.libcamera.org","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}},{"id":22593,"web_url":"https://patchwork.libcamera.org/comment/22593/","msgid":"","date":"2022-04-05T23:22:07","subject":"Re: [libcamera-devel] [PATCH v2 3/5] provide a default fixed-sized\n\tSpan constructor","submitter":{"id":111,"url":"https://patchwork.libcamera.org/api/people/111/","name":"Christian Rauch","email":"Rauch.Christian@gmx.de"},"content":"Hi Laurent,\n\nIf we can only default-construct a Span that is either 0-fixed-sized or\nvariable-sized, and we want to return default-constructed objects to\nindicate errors, then it is not possible to use N-fixed-size Spans.\n\nWe either have to use a Span type that supports N-fixed-sized\ndefault-construction, or the default-construction of types has to be\navoided. If having feature/behaviour comparability with std::span is a\nhigh priority, then only the option that avoids default-construction is\nleft.\n\nBest,\nChristian\n\n\nAm 05.04.22 um 17:27 schrieb Laurent Pinchart:\n> Hi Christian,\n>\n> Thank you for the patch.\n>\n> On Tue, Apr 05, 2022 at 01:42:13AM +0100, Christian Rauch via libcamera-devel wrote:\n>> This allows to construct empty 0-fixed-sized Spans.\n>>\n>> Signed-off-by: Christian Rauch \n>> ---\n>> include/libcamera/base/span.h | 2 --\n>> include/libcamera/controls.h | 2 +-\n>> 2 files changed, 1 insertion(+), 3 deletions(-)\n>>\n>> diff --git a/include/libcamera/base/span.h b/include/libcamera/base/span.h\n>> index 88d2e3de..bff4c115 100644\n>> --- a/include/libcamera/base/span.h\n>> +++ b/include/libcamera/base/span.h\n>> @@ -105,8 +105,6 @@ public:\n>>\n>> \tstatic constexpr std::size_t extent = Extent;\n>>\n>> -\ttemplate> -\t\t typename = std::enable_if_t>\n>\n> The issue here is that the std::span class has this constraint ([1]):\n>\n> This overload participates in overload resolution only if\n> extent == 0 || extent == std::dynamic_extent.\n>\n> [1] https://en.cppreference.com/w/cpp/container/span/span\n>\n> If we drop the constraint here, we will have an issue when switching to\n> std::span in the future. Is there a way we could achieve the result\n> you're aiming for without this change ?\n>\n>> \tconstexpr Span() noexcept\n>> \t\t: data_(nullptr)\n>> \t{\n>> diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h\n>> index 665bcac1..de8a7770 100644\n>> --- a/include/libcamera/controls.h\n>> +++ b/include/libcamera/controls.h\n>> @@ -167,7 +167,7 @@ public:\n>>\n>> \t\tusing V = typename T::value_type;\n>> \t\tconst V *value = reinterpret_cast(data().data());\n>> -\t\treturn { value, numElements_ };\n>> +\t\treturn T{ value, numElements_ };\n>> \t}\n>>\n>> #ifndef __DOXYGEN__\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 96AEEC3256\n\tfor ;\n\tTue, 5 Apr 2022 23:22:10 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id BB53765644;\n\tWed, 6 Apr 2022 01:22:09 +0200 (CEST)","from mout.gmx.net (mout.gmx.net [212.227.17.22])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 772C26563F\n\tfor ;\n\tWed, 6 Apr 2022 01:22:08 +0200 (CEST)","from [192.168.1.209] ([92.10.251.63]) by mail.gmx.net (mrgmx105\n\t[212.227.17.168]) with ESMTPSA (Nemesis) id 1MgesG-1oC2ip3NxE-00h3CQ\n\tfor\n\t; 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