[cfe-dev] Use of Smart Pointers in LLVM Projects

[Eli Bendersky]

On Fri, Jul 18, 2014 at 12:06 PM, Jordan Rose <jordan_rose at apple.com> wrote:

> I don't have much to add here besides +1. I think using std::unique_ptr
> even for create* functions/methods is the right way to go.


+1 smart pointers here are a win in terms of safety and self-documentation.
I don't see why create* factories should be treated differently.

Eli




> Reid's point about an abstraction penalty is interesting, but I don't
> think we do ownership transfers often enough to actually see a performance
> hit. (Of course, in the non-transferring case we'd just pass the pointer,
> not a 'const std::unique_ptr &' or anything.)
>
> Jordan
>
>
> On Jul 17, 2014, at 16:21 , David Blaikie <dblaikie at gmail.com> wrote:
>
> > There seems to be some uncertainty about the use of smart pointers
> > (previously OwningPtr, now std::unique_ptr and std::shared_ptr
> > predominantly) in the LLVM project as a whole, so here's a thread to
> > discuss/clarify/etc the project preferences/direction with regard to
> > smart pointer usage.
> >
> > For some context, see discussions in LLVM r212403 and Clang r213307.
> >
> > The basic question here seems to be whether smart pointer ownership is
> > a direction we want to take the LLVM project in general.
> >
> > I've seen others contribute and have myself contributed many patches
> > moving towards smart pointer ownership (both in the pre-C++11 days of
> > OwningPtr, and much moreso in the post-C++11 world with
> > std::unique_ptr and std::shared_ptr being usable inside containers, as
> > return values, etc, allowing many more opportunities).
> >
> > std::unique_ptr's been used in LLD as far back as r153620.
> > std::unique_ptr appeared in LLVM shortly after the C++11 switch with
> > Ahmed's work to migrate the project from OwningPtr to std::unique_ptr
> > (starting with r202609 and ending with r211259). Originally OwningPtr
> > was added in r45261.
> > Something in the order of 60 changes across clang and LLVM mention
> > unique_ptr in their subject and migrate various APIs to use unique_ptr
> > for ownership. Many of which remove uses of explicit delete or helpers
> > like DeleteContainerPointers (and removing explicit dtors in many of
> > those cases).
> >
> > Are people OK with/prefer the use of owning smart pointers in APIs?
> > Are there places where you've found them to be too noisy/burdensome
> > and would rather use raw pointers or some other abstraction? Would you
> > prefer pre-commit review of such changes to adequately consider
> > alternatives (such as?)?
> >
> > Thanks,
> > - David
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>
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