[{"id":33657,"web_url":"https://patchwork.libcamera.org/comment/33657/","msgid":"","date":"2025-03-19T16:56:20","subject":"Re: [PATCH v2 01/17] libcamera: matrix: Replace SFINAE with\n\tstatic_asserts","submitter":{"id":216,"url":"https://patchwork.libcamera.org/api/people/216/","name":"Barnabás Pőcze","email":"barnabas.pocze@ideasonboard.com"},"content":"Hi\n\n\n2025. 03. 19. 17:11 keltezéssel, Stefan Klug írta:\n> SFINAE is difficult to read and not needed in these cases. Replace it\n> with static_asserts. The idea came from [1] where it is stated:\n> \n> \"The use of enable_if seems misguided to me. SFINAE is useful for the\n> situation where we consider multiple candidates for something (overloads\n> or class template specializations) and try to choose the correct one,\n> without causing compilation to fail.\"\n> \n> [1]: https://stackoverflow.com/questions/62109526/c-friend-template-that-use-sfinae\n> \n> Signed-off-by: Stefan Klug \n> \n> ---\n> \n> Changes in v2:\n> - Added this patch\n> ---\n> include/libcamera/internal/matrix.h | 42 ++++++++---------------------\n> 1 file changed, 11 insertions(+), 31 deletions(-)\n> \n> diff --git a/include/libcamera/internal/matrix.h b/include/libcamera/internal/matrix.h\n> index a055e6926c94..8399be583f28 100644\n> --- a/include/libcamera/internal/matrix.h\n> +++ b/include/libcamera/internal/matrix.h\n> @@ -19,14 +19,11 @@ namespace libcamera {\n> \n> LOG_DECLARE_CATEGORY(Matrix)\n> \n> -#ifndef __DOXYGEN__\n> -template -\t std::enable_if_t> * = nullptr>\n> -#else\n> template\n> -#endif /* __DOXYGEN__ */\n> class Matrix\n> {\n> +\tstatic_assert(std::is_arithmetic_v, \"Matrix type must be arithmetic\");\n\nHere I agree with this change since there are no template specializations, etc.\nYou could also add `Rows > 0` and `Cols > 0` potentially. ANd I think the same\nshould be done with `Vector` as well.\n\n\n> +\n> public:\n> \tMatrix()\n> \t{\n> @@ -78,13 +75,10 @@ public:\n> \t\treturn Span{ &data_.data()[i * Cols], Cols };\n> \t}\n> \n> -#ifndef __DOXYGEN__\n> -\ttemplate>>\n> -#else\n> \ttemplate\n> -#endif /* __DOXYGEN__ */\n> -\tMatrix &operator*=(U d)\n> +\tconstexpr Matrix &operator*=(U d)\n> \t{\n> +\t\tstatic_assert(std::is_arithmetic_v, \"Multiplier must be arithmetic\");\n> \t\tfor (unsigned int i = 0; i < Rows * Cols; i++)\n> \t\t\tdata_[i] *= d;\n> \t\treturn *this;\n> @@ -94,14 +88,10 @@ private:\n> \tstd::array data_;\n> };\n> \n> -#ifndef __DOXYGEN__\n> -template -\t std::enable_if_t> * = nullptr>\n> -#else\n> template\n> -#endif /* __DOXYGEN__ */\n> -Matrix operator*(T d, const Matrix &m)\n> +constexpr Matrix operator*(T d, const Matrix &m)\n\nBut here, where this change concerns free function operators, I am not sure,\nhere multiple overloads existing does not seem that far-fetched of an idea.\nBut since this is an internal type and no such use case exists at the moment\nI think it is fine, just wanted to mention it.\n\n\nRegards,\nBarnabás Pőcze\n\n\n> {\n> +\tstatic_assert(std::is_arithmetic_v, \"Multiplier must be arithmetic\");\n> \tMatrix result;\n> \n> \tfor (unsigned int i = 0; i < Rows; i++) {\n> @@ -112,27 +102,17 @@ Matrix operator*(T d, const Matrix &m)\n> \treturn result;\n> }\n> \n> -#ifndef __DOXYGEN__\n> -template -\t std::enable_if_t> * = nullptr>\n> -#else\n> template\n> -#endif /* __DOXYGEN__ */\n> -Matrix operator*(const Matrix &m, T d)\n> +constexpr Matrix operator*(const Matrix &m, T d)\n> {\n> +\tstatic_assert(std::is_arithmetic_v, \"Multiplier must be arithmetic\");\n> \treturn d * m;\n> }\n> \n> -#ifndef __DOXYGEN__\n> -template -\t unsigned int R1, unsigned int C1,\n> -\t unsigned int R2, unsigned int C2,\n> -\t std::enable_if_t * = nullptr>\n> -#else\n> -template\n> -#endif /* __DOXYGEN__ */\n> -Matrix operator*(const Matrix &m1, const Matrix &m2)\n> +template\n> +constexpr Matrix operator*(const Matrix &m1, const Matrix &m2)\n> {\n> +\tstatic_assert(C1 == R2, \"Matrix dimensions must match for multiplication\");\n> \tMatrix result;\n> \n> \tfor (unsigned int i = 0; i < R1; i++) {","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 5949DC3301\n\tfor ;\n\tWed, 19 Mar 2025 16:56:28 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id ADE3B68945;\n\tWed, 19 Mar 2025 17:56:27 +0100 (CET)","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 974E8687FA\n\tfor ;\n\tWed, 19 Mar 2025 17:56:25 +0100 (CET)","from [192.168.33.18] (185.221.143.221.nat.pool.zt.hu\n\t[185.221.143.221])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id 7D68755A\n\tfor ;\n\tWed, 19 Mar 2025 17:54:42 +0100 (CET)"],"Authentication-Results":"lancelot.ideasonboard.com; dkim=pass (1024-bit key;\n\tunprotected) header.d=ideasonboard.com header.i=@ideasonboard.com\n\theader.b=\"ihmyrC0M\"; dkim-atps=neutral","DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1742403282;\n\tbh=D/KcFHGohE912p6E+8Ih/YgXldFnVf8sDC+wD6C4WJw=;\n\th=Date:Subject:To:References:From:In-Reply-To:From;\n\tb=ihmyrC0MXO/BLqiBPhdyT21N5sVGmOL8ysUiT406Av5vDY4fAnh432DTOgLNopuFi\n\tFEj22KKTaWaKjQ+1HUCOvDULa5uYHDVE+htEH3KfHXh1rgKbyYMo2UwpI2jRizNT6j\n\tj15B5k48n7oKj1mhJkGpgl+U7AIwfqvBvjmDG338=","Message-ID":"","Date":"Wed, 19 Mar 2025 17:56:20 +0100","MIME-Version":"1.0","User-Agent":"Mozilla Thunderbird","Subject":"Re: [PATCH v2 01/17] libcamera: matrix: Replace SFINAE with\n\tstatic_asserts","To":"libcamera-devel@lists.libcamera.org","References":"<20250319161152.63625-1-stefan.klug@ideasonboard.com>\n\t<20250319161152.63625-2-stefan.klug@ideasonboard.com>","From":"=?utf-8?q?Barnab=C3=A1s_P=C5=91cze?= ","Content-Language":"en-US, hu-HU","In-Reply-To":"<20250319161152.63625-2-stefan.klug@ideasonboard.com>","Content-Type":"text/plain; charset=UTF-8; format=flowed","Content-Transfer-Encoding":"8bit","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","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}},{"id":33823,"web_url":"https://patchwork.libcamera.org/comment/33823/","msgid":"<20250401005513.GO14432@pendragon.ideasonboard.com>","date":"2025-04-01T00:55:13","subject":"Re: [PATCH v2 01/17] libcamera: matrix: Replace SFINAE with\n\tstatic_asserts","submitter":{"id":2,"url":"https://patchwork.libcamera.org/api/people/2/","name":"Laurent Pinchart","email":"laurent.pinchart@ideasonboard.com"},"content":"On Wed, Mar 19, 2025 at 05:56:20PM +0100, Barnabás Pőcze wrote:\n> 2025. 03. 19. 17:11 keltezéssel, Stefan Klug írta:\n> > SFINAE is difficult to read and not needed in these cases. Replace it\n> > with static_asserts. The idea came from [1] where it is stated:\n> > \n> > \"The use of enable_if seems misguided to me. SFINAE is useful for the\n> > situation where we consider multiple candidates for something (overloads\n> > or class template specializations) and try to choose the correct one,\n> > without causing compilation to fail.\"\n> > \n> > [1]: https://stackoverflow.com/questions/62109526/c-friend-template-that-use-sfinae\n> > \n> > Signed-off-by: Stefan Klug \n> > \n> > ---\n> > \n> > Changes in v2:\n> > - Added this patch\n> > ---\n> > include/libcamera/internal/matrix.h | 42 ++++++++---------------------\n> > 1 file changed, 11 insertions(+), 31 deletions(-)\n> > \n> > diff --git a/include/libcamera/internal/matrix.h b/include/libcamera/internal/matrix.h\n> > index a055e6926c94..8399be583f28 100644\n> > --- a/include/libcamera/internal/matrix.h\n> > +++ b/include/libcamera/internal/matrix.h\n> > @@ -19,14 +19,11 @@ namespace libcamera {\n> > \n> > LOG_DECLARE_CATEGORY(Matrix)\n> > \n> > -#ifndef __DOXYGEN__\n> > -template > -\t std::enable_if_t> * = nullptr>\n> > -#else\n> > template\n> > -#endif /* __DOXYGEN__ */\n> > class Matrix\n> > {\n> > +\tstatic_assert(std::is_arithmetic_v, \"Matrix type must be arithmetic\");\n> \n> Here I agree with this change since there are no template specializations, etc.\n> You could also add `Rows > 0` and `Cols > 0` potentially. ANd I think the same\n> should be done with `Vector` as well.\n> \n> > +\n> > public:\n> > \tMatrix()\n> > \t{\n> > @@ -78,13 +75,10 @@ public:\n> > \t\treturn Span{ &data_.data()[i * Cols], Cols };\n> > \t}\n> > \n> > -#ifndef __DOXYGEN__\n> > -\ttemplate>>\n> > -#else\n> > \ttemplate\n> > -#endif /* __DOXYGEN__ */\n> > -\tMatrix &operator*=(U d)\n> > +\tconstexpr Matrix &operator*=(U d)\n> > \t{\n> > +\t\tstatic_assert(std::is_arithmetic_v, \"Multiplier must be arithmetic\");\n> > \t\tfor (unsigned int i = 0; i < Rows * Cols; i++)\n> > \t\t\tdata_[i] *= d;\n> > \t\treturn *this;\n> > @@ -94,14 +88,10 @@ private:\n> > \tstd::array data_;\n> > };\n> > \n> > -#ifndef __DOXYGEN__\n> > -template > -\t std::enable_if_t> * = nullptr>\n> > -#else\n> > template\n> > -#endif /* __DOXYGEN__ */\n> > -Matrix operator*(T d, const Matrix &m)\n> > +constexpr Matrix operator*(T d, const Matrix &m)\n> \n> But here, where this change concerns free function operators, I am not sure,\n> here multiple overloads existing does not seem that far-fetched of an idea.\n> But since this is an internal type and no such use case exists at the moment\n> I think it is fine, just wanted to mention it.\n\nSample code that exhibits the issue:\n\n--------\n#include \n#include \n\ntemplate\nT foo(T a, double b)\n{\n static_assert(std::is_same_v, \"Must be int\");\n return a * b;\n}\n\ntemplate\nT foo(T a, T b)\n{\n return a / b;\n}\n\nint main()\n{\n int a = foo(3, 2.0);\n double b = foo(3.0, 2.0);\n\n std::cout << a << \" \" << b << std::endl;\n\n return 0;\n}\n--------\n\n$ g++ -W -Wall -o sfinae2 sfinae2.cpp \nsfinae2.cpp: In function ‘int main()’:\nsfinae2.cpp:20:23: error: call of overloaded ‘foo(double, double)’ is ambiguous\n 20 | double b = foo(3.0, 2.0);\n | ~~~^~~~~~~~~~\nsfinae2.cpp:5:3: note: candidate: ‘T foo(T, double) [with T = double]’\n 5 | T foo(T a, double b)\n | ^~~\nsfinae2.cpp:12:3: note: candidate: ‘T foo(T, T) [with T = double]’\n 12 | T foo(T a, T b)\n | ^~~\n$\n\n--------\n#include \n#include \n\ntemplate> * = nullptr>\nT foo(T a, double b)\n{\n return a * b;\n}\n\ntemplate\nT foo(T a, T b)\n{\n return a / b;\n}\n\nint main()\n{\n int a = foo(3, 2.0);\n double b = foo(3.0, 2.0);\n\n std::cout << a << \" \" << b << std::endl;\n\n return 0;\n}\n--------\n\n$ g++ -W -Wall -o sfinae2 sfinae2.cpp\n$\n\nI'd keep SFINAE for the operators. For the removal of SFINAE for the\nMatrix class itself,\n\nReviewed-by: Laurent Pinchart \n\n> > {\n> > +\tstatic_assert(std::is_arithmetic_v, \"Multiplier must be arithmetic\");\n> > \tMatrix result;\n> > \n> > \tfor (unsigned int i = 0; i < Rows; i++) {\n> > @@ -112,27 +102,17 @@ Matrix operator*(T d, const Matrix &m)\n> > \treturn result;\n> > }\n> > \n> > -#ifndef __DOXYGEN__\n> > -template > -\t std::enable_if_t> * = nullptr>\n> > -#else\n> > template\n> > -#endif /* __DOXYGEN__ */\n> > -Matrix operator*(const Matrix &m, T d)\n> > +constexpr Matrix operator*(const Matrix &m, T d)\n> > {\n> > +\tstatic_assert(std::is_arithmetic_v, \"Multiplier must be arithmetic\");\n> > \treturn d * m;\n> > }\n> > \n> > -#ifndef __DOXYGEN__\n> > -template > -\t unsigned int R1, unsigned int C1,\n> > -\t unsigned int R2, unsigned int C2,\n> > -\t std::enable_if_t * = nullptr>\n> > -#else\n> > -template\n> > -#endif /* __DOXYGEN__ */\n> > -Matrix operator*(const Matrix &m1, const Matrix &m2)\n> > +template\n> > +constexpr Matrix operator*(const Matrix &m1, const Matrix &m2)\n> > {\n> > +\tstatic_assert(C1 == R2, \"Matrix dimensions must match for multiplication\");\n> > \tMatrix result;\n> > \n> > \tfor (unsigned int i = 0; i < R1; i++) {","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 9E090C3213\n\tfor ;\n\tTue, 1 Apr 2025 00:55:40 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id A4FD16897A;\n\tTue, 1 Apr 2025 02:55:39 +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 8059662C66\n\tfor ;\n\tTue, 1 Apr 2025 02:55:38 +0200 (CEST)","from pendragon.ideasonboard.com (85-76-147-224-nat.elisa-mobile.fi\n\t[85.76.147.224])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id 634958DB;\n\tTue, 1 Apr 2025 02:53:46 +0200 (CEST)"],"Authentication-Results":"lancelot.ideasonboard.com; dkim=pass (1024-bit key;\n\tunprotected) header.d=ideasonboard.com header.i=@ideasonboard.com\n\theader.b=\"JYctuBVh\"; dkim-atps=neutral","DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1743468826;\n\tbh=xA4nlTEirCobljqXhpNafyDsfx8ndFarDoMbFeotzZo=;\n\th=Date:From:To:Cc:Subject:References:In-Reply-To:From;\n\tb=JYctuBVhF3QjqfQcSIlFGQdeSUsCLZ7xbUMmJuH0Pyy+djbxgRjcnNnJbBYvQzgE1\n\tpXhJZLWhz48fmFbktg5w2rAdIWlicspnQsiHu4jKileeoWSRQ3itSlo3j5e8ZZGVPw\n\tl5s7nutS1ff8MReFCi49dqLf1Cs8ysPQThIkDhGI=","Date":"Tue, 1 Apr 2025 03:55:13 +0300","From":"Laurent Pinchart ","To":"=?utf-8?q?Barnab=C3=A1s_P=C5=91cze?= ","Cc":"libcamera-devel@lists.libcamera.org","Subject":"Re: [PATCH v2 01/17] libcamera: matrix: Replace SFINAE with\n\tstatic_asserts","Message-ID":"<20250401005513.GO14432@pendragon.ideasonboard.com>","References":"<20250319161152.63625-1-stefan.klug@ideasonboard.com>\n\t<20250319161152.63625-2-stefan.klug@ideasonboard.com>\n\t","MIME-Version":"1.0","Content-Type":"text/plain; charset=utf-8","Content-Disposition":"inline","Content-Transfer-Encoding":"8bit","In-Reply-To":"","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","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}}]