llvm dev - Apr 2017 - RFC: Plan for removing components from namespace std::experimental

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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Sounds reasonable to me.  I believe expectations are set appropriately with the
experimental namespace, and the extra, experimental library that needs to be
linked in.

From: cfe-dev [mailto:cfe-dev-bounces at lists.llvm.org] On Behalf Of Marshall
Clow via cfe-dev
Sent: Monday, April 10, 2017 3:23 PM
To: cfe-dev at lists.llvm.org; llvm-dev at lists.llvm.org
Subject: [cfe-dev] RFC: Plan for removing components from namespace
std::experimental

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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I think regardless of who may or may not be using *experimental* stuff
there shouldn't be a level of guaranteed stability. As the name
implies it's not stable. It's a vehicle for testing things and
prototype implementations that can't make it into main. Show me
another project where experimental == guaranteed stability

On Tue, Apr 11, 2017 at 4:22 AM, 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
>
>
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>

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. :-)

-Dimitry
> 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
> 
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
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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
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/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
> > _______________________________________________
> > cfe-dev mailing list
> > cfe-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>
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On Mon, Apr 10, 2017 at 2:48 PM, Dimitry Andric <dimitry at andric.com>
wrote:
> 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. :-)
>
Well, no.
For example, std::experimental::string_view is header-only; there's no part
of it that lives in the  libc++experimental lib.  It's not the only one.

-- Marshall
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Will clang give warning or hint so that users know what's going on and what
they can do?

Regards,
chenwj

2017-04-11 4:22 GMT+08:00 Marshall Clow via llvm-dev <
llvm-dev at lists.llvm.org>:
> 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
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>

-- 

--
Wei-Ren Chen (陳韋任)
Homepage: https://people.cs.nctu.edu.tw/~chenwj
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On Mon, Apr 10, 2017 at 1:22 PM, Marshall Clow <mclow.lists at gmail.com>
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...
>
>
Now that we have branched for 6.0, we can do this. ;-)
I'll be rolling out details this week ....

-- Marshall
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This plan SGTM.

Thanks Marshall.

/Eric

On Wed, Jan 3, 2018 at 5:43 PM, Marshall Clow via cfe-dev <
cfe-dev at lists.llvm.org> wrote:
> On Mon, Apr 10, 2017 at 1:22 PM, Marshall Clow <mclow.lists at
gmail.com>
> 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...
>>
>>
> Now that we have branched for 6.0, we can do this. ;-)
> I'll be rolling out details this week ....
>
> -- Marshall
>
>
>
>
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>
>
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On Wed, Jan 3, 2018 at 4:43 PM, Marshall Clow <mclow.lists at gmail.com>
wrote:
> Now that we have branched for 6.0, we can do this. ;-)
> I'll be rolling out details this week ....
>
> See thread titled "HEADS UP: Dates for removing components from
namespace
std::experimental”.

TL;DR - they're all going away on 1-Feb.

-- Marshall
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