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

[Christopher Di Bella via cfe-dev]

I second Justin's suggestion, but would that happen in LLVM 5 or 6?

Just as something to consider, it may also cause spurious errors for people
who are relying on the at-version-stability of experimental libraries,
causing them to turn off warnings for deprecated code.

As C Bergstrom has said, users buy into experimental libraries with the
knowledge that the interface or behaviour could change at a moment's
notice, so it might not be an issue, but it is worth considering.

On Tue., 11 Apr. 2017, 08:11 Justin Bogner via cfe-dev, <
cfe-dev at lists.llvm.org> wrote:

> 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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