Comment 57 for bug 345207

(In reply to comment #37)
> >+class SVGLengthListHelper
> >+{
> >+ nsCOMPtr<nsIDOMSVGLengthList> mList;
> >+ PRUint32 mCount;
> >+public:
> >+ SVGLengthListHelper(const already_AddRefed<nsIDOMSVGLengthList> list);
>
> I don't think you can use already_AddRefed as a function argument. AFAIK that
> construct is only for return values. You want to make the argument a raw
> pointer and probably use already_AddRefed when you call it.

Yes, on further research (bug #172030), |already_AddRefed<T>| is used as a temporary _short_ lived return value.

Also (bug #178187), using the raw pointer result of already_AddRefed<T>::get() doesn't make clear the transfer of ownership.

I struggled with this for a while because I wanted the ownership to be inside the helper class. Rather than extract and pass the raw pointer it might be clearer to keep the ownership outside of the class.