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

Justin Bogner via llvm-dev llvm-dev at lists.llvm.org
Mon Apr 10 15:10:51 PDT 2017

Marshall Clow via cfe-dev <cfe-dev at lists.llvm.org> writes:
> 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

Should we throw [[deprecated("use std::filesystem")]] and such on these
things in the window between the non-experimental version being released
and the experimental one being removed?

> and probably other things...
> Comments?
> -- Marshall
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