[llvm-dev] [cfe-dev] RFC: Plan for removing components from namespace std::experimental

Dimitry Andric via llvm-dev llvm-dev at lists.llvm.org
Mon Apr 10 14:48:13 PDT 2017

Yes, this seems a good idea.  I think it is already clear enough that the experimental headers can't be relied upon for any long term, so having a specific cutoff date in there is good.  Maybe even mention it in the respective headers?

That said, on FreeBSD I didn't get any requests for adding the libc++experimental dynamic library, so I have simply omitted it.  Therefore, at least on FreeBSD there are no users of these features, so they won't be able to miss them either. :-)


> On 10 Apr 2017, at 22:22, Marshall Clow via cfe-dev <cfe-dev at lists.llvm.org> wrote:
> As part of the work on C++17, WG21 released a series of "Technical Specifications", (TS) which added proposed new features to the standard library. These were all defined in the namespace 'std::experimental' (and namespaces inside of that).
> Then, much of these features were merged into the main standard, and became part of namespace 'std'.  Libc++ now has two implementations of several of these, and they are diverging (because changes were made to the ones in the main standard, but not to the ones in the TS.
> In the long run, I would like to remove the TS versions of these features from libc++ - since there are "better" versions in the main standard now. However, since people are using these, I don't think yanking them w/o warning is the right thing to do.
> So, I'm proposing a new policy, and a timetable:
> One year.
> One year after we ship a LLVM release that supports a new C++ standard, we will remove all the features that are in the 'experimental' namespace that are implemented in the new standard).
> Applying this policy to C++17,  we get:
> LLVM 5.0 will support C++17.
> So, for LLVM 7.0, we will remove (at least) the following features from libc++
> * std::experimental::filesystem
> * std::experimental::optional
> * std::experimental::any
> * std::experimental::string_view
> * the searchers (std::experimental::boyer_moore, etc)
> * std::experimental::random_shuffle
> and probably other things...
> Comments?
> -- Marshall
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> cfe-dev at lists.llvm.org
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