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authorLaurent Pinchart <laurent.pinchart@ideasonboard.com>2022-08-30 05:45:01 +0300
committerLaurent Pinchart <laurent.pinchart@ideasonboard.com>2022-08-31 13:58:00 +0300
commit48d7bb29bd69c260bc5f9c104f6270dad4564b0d (patch)
tree4a4721c801e3417341b9c131d5016e010bb92030 /utils
parent084799bcadf204d84a5f383aa893e4052b36e7aa (diff)
libcamera: base: signal: Disable connect() for functor if args mismatch
If a pointer-to-member is passed to the Signal::connect() function with arguments that don't match the Signal type, the pointer-to-member version of connect() will not match during template argument resolution, but the functor version will. This results in a compilation error in the BoundMethodFunctor class, due to the pointer-to-member not being a functor and thus not being callable directly. The error messages are quite cryptic. With the following error applied, diff --git a/test/signal.cpp b/test/signal.cpp index 5c6b304dac0b..6dd11ac45313 100644 --- a/test/signal.cpp +++ b/test/signal.cpp @@ -107,6 +107,7 @@ protected: /* Test signal emission and reception. */ called_ = false; signalVoid_.connect(this, &SignalTest::slotVoid); + signalVoid_.connect(this, &SignalTest::slotInteger1); signalVoid_.emit(); if (!called_) { gcc outputs ../../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 = {}]’: ../../include/libcamera/base/bound_method.h:143:4: required from here ../../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 t::*)(int)>*)this)->libcamera::BoundMethodFunctor<SignalTest, void, void (SignalTest::*)(int)>::func_) (...)’ 146 | return func_(args...); | ~~~~~^~~~~~~~~ and clang isn't much better: ../../include/libcamera/base/bound_method.h:146:11: error: called object type 'void (SignalTest::*)(int)' is not a function or function pointer return func_(args...); ^~~~~ ../../include/libcamera/base/bound_method.h:137:2: note: in instantiation of member function 'libcamera::BoundMethodFunctor<SignalTest, void, void (SignalTest::*)(int)>::activate' requested here BoundMethodFunctor(T *obj, Object *object, Func func, ^ ../../include/libcamera/base/signal.h:80:27: note: in instantiation of member function 'libcamera::BoundMethodFunctor<SignalTest, void, void (SignalTest::*)(int)>::BoundMethodFunctor' requested here SignalBase::connect(new BoundMethodFunctor<T, void, Func, Args...>(obj, nullptr, func)); ^ ../../test/signal.cpp:110:15: note: in instantiation of function template specialization 'libcamera::Signal<>::connect<SignalTest, void (SignalTest::*)(int), nullptr>' requested here signalVoid_.connect(this, &SignalTest::slotInteger1); ^ Improve error reporting by disabling the functor version of connect() when the Func argument isn't invocable with the Signal arguments. gcc will then complain with ../../test/signal.cpp:110:36: error: no matching function for call to ‘libcamera::Signal<>::connect(SignalTest*, void (SignalTest::*)(int))’ 110 | signalVoid_.connect(this, &SignalTest::slotInteger1); | ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ and clang with ../../test/signal.cpp:110:15: error: no matching member function for call to 'connect' signalVoid_.connect(this, &SignalTest::slotInteger1); ~~~~~~~~~~~~^~~~~~~ which are more readable. This change requires usage of std::is_invocable<>, which is only available starting in C++17. This is fine for usage of the Signal class within libcamera, as the project is compiled with C++17, but we try to keep the public API compatible C++14. Condition the additional checks based on the C++ version. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Paul Elder <paul.elder@ideasonboard.com> Acked-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
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