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

[Eric Christopher]

Sounds like we've got sufficient amount of momentum here for Dave to
go ahead and recommit. Any last objections?

-eric

On Fri, Jul 18, 2014 at 1:35 PM, Eli Bendersky <eliben at google.com> wrote:
>
>
>
> 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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