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

[C Bergström via llvm-dev]

Two points and this my be more philosophy

#1 Is having the duplicate functionality bad for whoever is a user of
the experimental version? iow is it a disservice to keeping it for any
period of time? If so why would anyone advocate anything except
immediate deprecation or removal?

#2 How did this happen and why didn't anyone notice? (Apologies if
putting anyone on the spot and not my intention) Does it raise
questions about how the experimental namespace and stuff should be
managed.

I think less overhead will encourage innovation on experimental stuff.
When /you/ start adding maintenance burdens or guarantees, especially
for code which *you* aren't the maintainer it becomes unfun.




On Tue, Apr 11, 2017 at 6:27 AM, Christopher Di Bella via cfe-dev
<cfe-dev at lists.llvm.org> wrote:
> 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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