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e07aa30b4b
Forward declaring functions with default arguments is difficult. If you try to say:
template<typename T>
inline void
CycleCollectionNoteChild(nsCycleCollectionTraversalCallback& aCallback,
T* aChild, const char* aName, uint32_t aFlags);
and then later have:
template<typename T>
inline void
CycleCollectionNoteChild(nsCycleCollectionTraversalCallback& aCallback,
T* aChild, const char* aName, uint32_t aFlags = 0);
{
...
}
the compiler complains that default arguments cannot be added to a
function template that has already been declared. If you attempt to
mollify the compiler by declaring instead:
template<typename T>
inline void
CycleCollectionNoteChild(nsCycleCollectionTraversalCallback& aCallback,
T* aChild, const char* aName, uint32_t aFlags = 0);
the compiler then complains about redefining the default argument (!)
when an actual definition is found.
To circumvent this, manually implement "default" arguments by providing
a three-argument form of CycleCollectionNoteChild, which simply forwards
to the four-argument version.
102 lines
3.3 KiB
C++
102 lines
3.3 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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// This header will be included by headers that define refpointer and array classes
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// in order to specialize CC helpers such as ImplCycleCollectionTraverse for them.
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#ifndef nsCycleCollectionNoteChild_h__
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#define nsCycleCollectionNoteChild_h__
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#include "nsCycleCollectionTraversalCallback.h"
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#include "mozilla/Likely.h"
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#include "mozilla/TypeTraits.h"
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enum
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{
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CycleCollectionEdgeNameArrayFlag = 1
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};
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// Just a helper for appending "[i]". Didn't want to pull in string headers here.
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void
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CycleCollectionNoteEdgeNameImpl(nsCycleCollectionTraversalCallback& aCallback,
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const char* aName,
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uint32_t aFlags = 0);
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// Should be inlined so that in the no-debug-info case this is just a simple if().
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MOZ_ALWAYS_INLINE void
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CycleCollectionNoteEdgeName(nsCycleCollectionTraversalCallback& aCallback,
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const char* aName,
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uint32_t aFlags = 0)
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{
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if (MOZ_UNLIKELY(aCallback.WantDebugInfo())) {
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CycleCollectionNoteEdgeNameImpl(aCallback, aName, aFlags);
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}
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}
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#define NS_CYCLE_COLLECTION_INNERCLASS \
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cycleCollection
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#define NS_CYCLE_COLLECTION_INNERNAME \
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_cycleCollectorGlobal
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#define NS_CYCLE_COLLECTION_PARTICIPANT(_class) \
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_class::NS_CYCLE_COLLECTION_INNERCLASS::GetParticipant()
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template<typename T>
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nsISupports*
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ToSupports(T* aPtr, typename T::NS_CYCLE_COLLECTION_INNERCLASS* aDummy = 0)
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{
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return T::NS_CYCLE_COLLECTION_INNERCLASS::Upcast(aPtr);
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}
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// The default implementation of this class template is empty, because it
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// should never be used: see the partial specializations below.
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template<typename T,
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bool IsXPCOM = mozilla::IsBaseOf<nsISupports, T>::value>
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struct CycleCollectionNoteChildImpl
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{
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};
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template<typename T>
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struct CycleCollectionNoteChildImpl<T, true>
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{
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static void Run(nsCycleCollectionTraversalCallback& aCallback, T* aChild)
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{
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aCallback.NoteXPCOMChild(ToSupports(aChild));
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}
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};
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template<typename T>
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struct CycleCollectionNoteChildImpl<T, false>
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{
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static void Run(nsCycleCollectionTraversalCallback& aCallback, T* aChild)
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{
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aCallback.NoteNativeChild(aChild, NS_CYCLE_COLLECTION_PARTICIPANT(T));
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}
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};
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// We declare CycleCollectionNoteChild in 3-argument and 4-argument variants,
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// rather than using default arguments, so that forward declarations work
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// regardless of header inclusion order.
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template<typename T>
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inline void
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CycleCollectionNoteChild(nsCycleCollectionTraversalCallback& aCallback,
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T* aChild, const char* aName, uint32_t aFlags)
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{
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CycleCollectionNoteEdgeName(aCallback, aName, aFlags);
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CycleCollectionNoteChildImpl<T>::Run(aCallback, aChild);
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}
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template<typename T>
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inline void
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CycleCollectionNoteChild(nsCycleCollectionTraversalCallback& aCallback,
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T* aChild, const char* aName)
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{
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CycleCollectionNoteChild(aCallback, aChild, aName, 0);
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}
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#endif // nsCycleCollectionNoteChild_h__
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