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The initial approach for providing public access to native interfaces via T::nativeInteface<I>() was based on the template not being defined, and then having explicit instantiations of the supported types in a source file, so that the accessors were exported and available to the user. This worked fine for "simple" types such as QOpenGLContext and QOffscreenSurface, but presented a problem in the context of classes with subclasses, such as Q{Core,Gui}Application. To ensure that a native interface for QCoreApplication was accessible both from QCoreApplication and its subclasses, while at the same time preventing a native interface for QGuiApplication to be accessible for QCoreApplication, the nativeInterface() template function had to be declared in each subclass. Which in turn meant specializing each native interface once for each subclass it was available in. This quickly became tedious to manage, and the requirements for exposing a new native interface wasn't very clear with all these template specializations and explicit instantiations spread around. To improve on this situation, while also squashing a few other birds at the same time, we change the approach to use type erasure. The definition of T::nativeInteface<I>() is now inline, passing on the requested interface to a per type (T, not I) helper function, with the interface type flattened to a std::type_info. The type_info requested by the user is then compared to the available types in a single per-type (T) "switch statement", which is a lot easier to follow for someone trying to trace the logic of how a native interface is resolved. We can safely rely on type_info being stable between the user application and the Qt library as a result of exporting the type info for each native interface, by explicitly ensuring they have a key function. This is the same mechanism that ensures we can safely dynamic_cast these interfaces, even across library boundaries. The use of a free standing templated helper function instead of a member function in the type T, is to avoid shadowing issues, and to not pollute the class namespace of T with the helper function. Since we are already changing the plumbing for how a user resolves a native interface for a type T, we take the opportunity to add a few extra safeguards to the machinery. First, we add a static assert in the T::nativeInteface<I>() definition, that ensures that only compatible interfaces, as declared by the interface themselves, are allowed. This ensures a compile time error when an incompatible interface is requested, which improves on the link time errors we had prior to this patch, and also offsets the one downside of type erasure, namely that errors are only caught at runtime. Secondly, each interface meant for public consumption through T::nativeInteface<I>() is declared with a revision, which is checked when requesting the interface. This allows us to bump the revision when we make breaking changes to the interface that would have otherwise been binary incompatible. Since the user will never see this interface due to the revision check, they will not end up calling methods that have been removed or renamed. One advantage of moving to a type-erased approach for the plumbing is that we're not longer exposing the native interface types as part of the T::nativeInteface symbols. This means that if we ever want to rename a native interface, the only exported symbol that the user code relies on is the type info. Renaming is then possible by just exporting the type info for the old interface, but leaving it empty. Since no class in Qt implements the old native interface, the user will just get a nullptr back, similarly to bumping the revision of an interface. Change-Id: Ie50d8fb536aafe2836370caacb22afbcfaf1712a Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io> |
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auto | ||
baselineserver | ||
benchmarks | ||
global | ||
libfuzzer | ||
manual | ||
shared | ||
testserver | ||
CMakeLists.txt | ||
README |
This directory contains autotests and benchmarks based on Qt Test. In order to run the autotests reliably, you need to configure a desktop to match the test environment that these tests are written for. Linux X11: * The user must be logged in to an active desktop; you can't run the autotests without a valid DISPLAY that allows X11 connections. * The tests are run against a KDE3 or KDE4 desktop. * Window manager uses "click to focus", and not "focus follows mouse". Many tests move the mouse cursor around and expect this to not affect focus and activation. * Disable "click to activate", i.e., when a window is opened, the window manager should automatically activate it (give it input focus) and not wait for the user to click the window.