/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ /* vim: set ts=8 sts=2 et sw=2 tw=80: */ /* This Source Code Form is subject to the terms of the Mozilla Public * License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/** * This header file provides macros which help you make your class implement * nsIClassInfo. Implementing nsIClassInfo is particularly helpful if you have * a C++ class which implements multiple interfaces and which you access from * JavaScript. If that class implements nsIClassInfo, the JavaScript code * won't have to call QueryInterface on instances of the class; all methods * from all interfaces returned by GetInterfaces() will be available * automagically. * * Here's all you need to do. Given a class * * class nsFooBar : public nsIFoo, public nsIBar { }; * * you should already have the following nsISupports implementation in its cpp * file: * * NS_IMPL_ISUPPORTS(nsFooBar, nsIFoo, nsIBar). * * Change this to * * NS_IMPL_CLASSINFO(nsFooBar, nullptr, 0, NS_FOOBAR_CID) * NS_IMPL_ISUPPORTS_CI(nsFooBar, nsIFoo, nsIBar) * * If nsFooBar is threadsafe, change the 0 above to nsIClassInfo::THREADSAFE. * If it's a singleton, use nsIClassInfo::SINGLETON. The full list of flags is * in nsIClassInfo.idl. * * The nullptr parameter is there so you can pass a function for converting * from an XPCOM object to a scriptable helper. Unless you're doing * specialized JS work, you can probably leave this as nullptr. * * This file also defines the NS_IMPL_QUERY_INTERFACE_CI macro, which you can * use to replace NS_IMPL_QUERY_INTERFACE, if you use that instead of * NS_IMPL_ISUPPORTS. * * That's it! The rest is gory details. * * * Notice that nsFooBar didn't need to inherit from nsIClassInfo in order to * "implement" it. However, after adding these macros to nsFooBar, you you can * QueryInterface an instance of nsFooBar to nsIClassInfo. How can this be? * * The answer lies in the NS_IMPL_ISUPPORTS_CI macro. It modifies nsFooBar's * QueryInterface implementation such that, if we ask to QI to nsIClassInfo, it * returns a singleton object associated with the class. (That singleton is * defined by NS_IMPL_CLASSINFO.) So all nsFooBar instances will return the * same object when QI'ed to nsIClassInfo. (You can see this in * NS_IMPL_QUERY_CLASSINFO below.) * * This hack breaks XPCOM's rules, since if you take an instance of nsFooBar, * QI it to nsIClassInfo, and then try to QI to nsIFoo, that will fail. On the * upside, implementing nsIClassInfo doesn't add a vtable pointer to instances * of your class. * * In principal, you can also implement nsIClassInfo by inheriting from the * interface. But some code expects that when it QI's an object to * nsIClassInfo, it gets back a singleton which isn't attached to any * particular object. If a class were to implement nsIClassInfo through * inheritance, that code might QI to nsIClassInfo and keep the resulting * object alive, thinking it was only keeping alive the classinfo singleton, * but in fact keeping a whole instance of the class alive. See, e.g., bug * 658632. * * Unless you specifically need to have a different nsIClassInfo instance for * each instance of your class, you should probably just implement nsIClassInfo * as a singleton.
*/
class GenericClassInfo : public nsIClassInfo { public: struct ClassInfoData { // This function pointer uses NS_CALLBACK_ because it's always set to an // NS_IMETHOD function, which uses __stdcall on Win32. typedef NS_CALLBACK_(nsresult, GetInterfacesProc)(nsTArray<nsIID>& aArray);
GetInterfacesProc getinterfaces;
// This function pointer doesn't use NS_CALLBACK_ because it's always set to // a vanilla function. typedef nsresult (*GetScriptableHelperProc)(nsIXPCScriptable** aHelper);
GetScriptableHelperProc getscriptablehelper;
// Note that this macro is an internal implementation of this header and // should not be used outside it. It does not end the interface map as this // is done in NS_IMPL_QUERY_INTERFACE_CI or the _INHERITED variant. #define NS_IMPL_QUERY_INTERFACE_CI_GUTS(aClass, ...) \
static_assert(MOZ_ARG_COUNT(__VA_ARGS__) > 0, \ "Need more arguments to NS_IMPL_QUERY_INTERFACE_CI"); \
NS_INTERFACE_MAP_BEGIN(aClass) \
MOZ_FOR_EACH(NS_INTERFACE_MAP_ENTRY, (), (__VA_ARGS__)) \
NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, MOZ_ARG_1(__VA_ARGS__)) \
NS_IMPL_QUERY_CLASSINFO(aClass)
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