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Bug 1097861 - make CycleCollectionNoteChild more easily forward-declarable; r=mccr8

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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.
This commit is contained in:
Nathan Froyd 2014-11-12 15:22:32 -05:00
parent b2fec0fb4a
commit e07aa30b4b
1 changed files with 12 additions and 1 deletions
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13
xpcom/glue/nsCycleCollectionNoteChild.h
View File

@ -78,13 +78,24 @@ struct CycleCollectionNoteChildImpl<T, false>
}
};
// We declare CycleCollectionNoteChild in 3-argument and 4-argument variants,
// rather than using default arguments, so that forward declarations work
// regardless of header inclusion order.
template<typename T>
inline void
CycleCollectionNoteChild(nsCycleCollectionTraversalCallback& aCallback,
T* aChild, const char* aName, uint32_t aFlags = 0)
T* aChild, const char* aName, uint32_t aFlags)
{
CycleCollectionNoteEdgeName(aCallback, aName, aFlags);
CycleCollectionNoteChildImpl<T>::Run(aCallback, aChild);
}
template<typename T>
inline void
CycleCollectionNoteChild(nsCycleCollectionTraversalCallback& aCallback,
T* aChild, const char* aName)
{
CycleCollectionNoteChild(aCallback, aChild, aName, 0);
}
#endif // nsCycleCollectionNoteChild_h__