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{ "id": 17248, "url": "https://patchwork.libcamera.org/api/patches/17248/?format=api", "web_url": "https://patchwork.libcamera.org/patch/17248/", "project": { "id": 1, "url": "https://patchwork.libcamera.org/api/projects/1/?format=api", "name": "libcamera", "link_name": "libcamera", "list_id": "libcamera_core", "list_email": "libcamera-devel@lists.libcamera.org", "web_url": "", "scm_url": "", "webscm_url": "" }, "msgid": "<20220830030615.29089-1-laurent.pinchart@ideasonboard.com>", "date": "2022-08-30T03:06:15", "name": "[libcamera-devel] libcamera: base: signal: Disable connect() for functor if args mismatch", "commit_ref": null, "pull_url": null, "state": "accepted", "archived": false, "hash": "730c2a4636e901c7b6dc7cc954e8adbe51534512", "submitter": { "id": 2, "url": "https://patchwork.libcamera.org/api/people/2/?format=api", "name": "Laurent Pinchart", "email": "laurent.pinchart@ideasonboard.com" }, "delegate": null, "mbox": "https://patchwork.libcamera.org/patch/17248/mbox/", "series": [ { "id": 3451, "url": "https://patchwork.libcamera.org/api/series/3451/?format=api", "web_url": "https://patchwork.libcamera.org/project/libcamera/list/?series=3451", "date": "2022-08-30T03:06:15", "name": "[libcamera-devel] libcamera: base: signal: Disable connect() for functor if args mismatch", "version": 1, "mbox": "https://patchwork.libcamera.org/series/3451/mbox/" } ], "comments": "https://patchwork.libcamera.org/api/patches/17248/comments/", "check": "pending", "checks": "https://patchwork.libcamera.org/api/patches/17248/checks/", "tags": {}, "headers": { "Return-Path": "<libcamera-devel-bounces@lists.libcamera.org>", "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 4D361C0DA4\n\tfor <parsemail@patchwork.libcamera.org>;\n\tTue, 30 Aug 2022 03:06:27 +0000 (UTC)", "from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 8E24C61FC1;\n\tTue, 30 Aug 2022 05:06:26 +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 5D8F2603E0\n\tfor <libcamera-devel@lists.libcamera.org>;\n\tTue, 30 Aug 2022 05:06:25 +0200 (CEST)", "from pendragon.ideasonboard.com (62-78-145-57.bb.dnainternet.fi\n\t[62.78.145.57])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id A139C4A8;\n\tTue, 30 Aug 2022 05:06:24 +0200 (CEST)" ], "DKIM-Signature": [ "v=1; 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dkim=pass (1024-bit key; \n\tunprotected) header.d=ideasonboard.com\n\theader.i=@ideasonboard.com\n\theader.b=\"Pyu737Wr\"; dkim-atps=neutral", "To": "libcamera-devel@lists.libcamera.org", "Date": "Tue, 30 Aug 2022 06:06:15 +0300", "Message-Id": "<20220830030615.29089-1-laurent.pinchart@ideasonboard.com>", "X-Mailer": "git-send-email 2.35.1", "MIME-Version": "1.0", "Content-Type": "text/plain; charset=UTF-8", "Content-Transfer-Encoding": "8bit", "Subject": "[libcamera-devel] [PATCH] libcamera: base: signal: Disable\n\tconnect() for functor if args mismatch", "X-BeenThere": "libcamera-devel@lists.libcamera.org", "X-Mailman-Version": "2.1.29", "Precedence": "list", "List-Id": "<libcamera-devel.lists.libcamera.org>", "List-Unsubscribe": "<https://lists.libcamera.org/options/libcamera-devel>,\n\t<mailto:libcamera-devel-request@lists.libcamera.org?subject=unsubscribe>", "List-Archive": "<https://lists.libcamera.org/pipermail/libcamera-devel/>", "List-Post": "<mailto:libcamera-devel@lists.libcamera.org>", "List-Help": "<mailto:libcamera-devel-request@lists.libcamera.org?subject=help>", "List-Subscribe": "<https://lists.libcamera.org/listinfo/libcamera-devel>,\n\t<mailto:libcamera-devel-request@lists.libcamera.org?subject=subscribe>", "From": "Laurent Pinchart via libcamera-devel\n\t<libcamera-devel@lists.libcamera.org>", "Reply-To": "Laurent Pinchart <laurent.pinchart@ideasonboard.com>", "Errors-To": "libcamera-devel-bounces@lists.libcamera.org", "Sender": "\"libcamera-devel\" <libcamera-devel-bounces@lists.libcamera.org>" }, "content": "If a pointer-to-member is passed to the Signal::connect() function with\narguments that don't match the Signal type, the pointer-to-member\nversion of connect() will not match during template argument resolution,\nbut the functor version will. This results in a compilation error in the\nBoundMethodFunctor class, due to the pointer-to-member not being a\nfunctor and thus not being callable directly. The error messages are\nquite cryptic. With the following error applied,", "diff": "diff --git a/test/signal.cpp b/test/signal.cpp\nindex 5c6b304dac0b..6dd11ac45313 100644\n--- a/test/signal.cpp\n+++ b/test/signal.cpp\n@@ -107,6 +107,7 @@ protected:\n \t\t/* Test signal emission and reception. */\n \t\tcalled_ = false;\n \t\tsignalVoid_.connect(this, &SignalTest::slotVoid);\n+\t\tsignalVoid_.connect(this, &SignalTest::slotInteger1);\n \t\tsignalVoid_.emit();\n\n \t\tif (!called_) {\n\ngcc outputs\n\n../../include/libcamera/base/bound_method.h: In instantiation of ‘R libcamera::BoundMethodFunctor<T, R, Func, Args>::activate(Args ..., bool) [with T = SignalTest; R = void; Func = void (SignalTest::*)(int); Args = {}]’:\n../../include/libcamera/base/bound_method.h:143:4: required from here\n../../include/libcamera/base/bound_method.h:146:37: error: must use ‘.*’ or ‘->*’ to call pointer-to-member function in ‘((libcamera::BoundMethodFunctor<SignalTest, void, void (SignalTest::*)(int)>*)this)->libcamera::BoundMethodFunctor<SignalTest, void, void (SignalTest::*)(int)>::func_ (...)’, e.g. ‘(... ->* ((libcamera::BoundMethodFunctor<SignalTest, void, void (SignalTes\nt::*)(int)>*)this)->libcamera::BoundMethodFunctor<SignalTest, void, void (SignalTest::*)(int)>::func_) (...)’\n 146 | return func_(args...);\n | ~~~~~^~~~~~~~~\n\nand clang isn't much better:\n\n../../include/libcamera/base/bound_method.h:146:11: error: called object type 'void (SignalTest::*)(int)' is not a function or function pointer\n return func_(args...);\n ^~~~~\n../../include/libcamera/base/bound_method.h:137:2: note: in instantiation of member function 'libcamera::BoundMethodFunctor<SignalTest, void, void (SignalTest::*)(int)>::activate' requested here\n BoundMethodFunctor(T *obj, Object *object, Func func,\n ^\n../../include/libcamera/base/signal.h:80:27: note: in instantiation of member function 'libcamera::BoundMethodFunctor<SignalTest, void, void (SignalTest::*)(int)>::BoundMethodFunctor' requested here\n SignalBase::connect(new BoundMethodFunctor<T, void, Func, Args...>(obj, nullptr, func));\n ^\n../../test/signal.cpp:110:15: note: in instantiation of function template specialization 'libcamera::Signal<>::connect<SignalTest, void (SignalTest::*)(int), nullptr>' requested here\n signalVoid_.connect(this, &SignalTest::slotInteger1);\n ^\n\nImprove error reporting by disabling the functor version of connect()\nwhen the Func argument isn't invocable with the Signal arguments. gcc\nwill then complain with\n\n../../test/signal.cpp:110:36: error: no matching function for call to ‘libcamera::Signal<>::connect(SignalTest*, void (SignalTest::*)(int))’\n 110 | signalVoid_.connect(this, &SignalTest::slotInteger1);\n | ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n\nand clang with\n\n../../test/signal.cpp:110:15: error: no matching member function for call to 'connect'\n signalVoid_.connect(this, &SignalTest::slotInteger1);\n ~~~~~~~~~~~~^~~~~~~\n\nwhich are more readable.\n\nThis change requires usage of std::is_invocable<>, which is only\navailable starting in C++17. This is fine for usage of the Signal class\nwithin libcamera, as the project is compiled with C++17, but we try to\nkeep the public API compatible C++14. Condition the additional checks\nbased on the C++ version.\n\nSigned-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>\n---\n include/libcamera/base/signal.h | 12 ++++++++++--\n 1 file changed, 10 insertions(+), 2 deletions(-)\n\ndiff --git a/include/libcamera/base/signal.h b/include/libcamera/base/signal.h\nindex efb591bc5073..841e4b4ca15c 100644\n--- a/include/libcamera/base/signal.h\n+++ b/include/libcamera/base/signal.h\n@@ -63,7 +63,11 @@ public:\n \n #ifndef __DOXYGEN__\n \ttemplate<typename T, typename Func,\n-\t\t std::enable_if_t<std::is_base_of<Object, T>::value> * = nullptr>\n+\t\t std::enable_if_t<std::is_base_of<Object, T>::value\n+#if __cplusplus >= 201703L\n+\t\t\t\t && std::is_invocable_v<Func, Args...>\n+#endif\n+\t\t\t\t > * = nullptr>\n \tvoid connect(T *obj, Func func, ConnectionType type = ConnectionTypeAuto)\n \t{\n \t\tObject *object = static_cast<Object *>(obj);\n@@ -71,7 +75,11 @@ public:\n \t}\n \n \ttemplate<typename T, typename Func,\n-\t\t std::enable_if_t<!std::is_base_of<Object, T>::value> * = nullptr>\n+\t\t std::enable_if_t<!std::is_base_of<Object, T>::value\n+#if __cplusplus >= 201703L\n+\t\t\t\t && std::is_invocable_v<Func, Args...>\n+#endif\n+\t\t\t\t > * = nullptr>\n #else\n \ttemplate<typename T, typename Func>\n #endif\n", "prefixes": [ "libcamera-devel" ] }