On Monday 2014-12-22 16:10 -0500, Jeff Muizelaar wrote: > We were talking about this problem and it was a bunch of work to figure out > the conclusion so I decided to write a summary: > > Replacing already_AddRefed with nsRefPtr causes allows two new things: > > nsRefPtr<T> getT(); > > 1. T* p = getT(); // this is unsafe because the destructor runs immediately > and p is left dangling > 2. foo(getT()); // this is safe > > Possible solutions would be to: > - remove implicit conversions to T* > - add operator T* explicit and operator T* && = delete // this will be > available in GCC 4.8.1 and MSVC 2014 Nov CTP
I think removing implicit conversions to T* will make a lot of code
in the tree uglier (".get()" everywhere). That might, in turn,
encourage people to do worse things to avoid having to write .get()
everywhere; it's worth thinking about what those things will be.
(I think it's also worth thinking about the *massive* number of
callsites that will need to be fixed if we remove implicit
conversion to T*.)
I'd also like to keep nsRefPtr and nsCOMPtr consistent with each
other in this regard, to avoid people having to learn additional
patterns. (And, on that subject, I think development practice in
MFBT has been too readily adding new and different things instead of
moving the existing things from XPCOM into MFBT and then improving
them incrementally.)
-David
--
𝄞 L. David Baron http://dbaron.org/ 𝄂
𝄢 Mozilla https://www.mozilla.org/ 𝄂
Before I built a wall I'd ask to know
What I was walling in or walling out,
And to whom I was like to give offense.
- Robert Frost, Mending Wall (1914)
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