[cfe-dev] The state of Concepts in Clang

Thu Feb 9 13:59:07 PST 2017

Hi Hubert,

> At this time, I have been working on Concepts in Clang.

Ah, great to know!

>  I am not sure how
> "people" are using concepts in GCC, but my experience on unit testing
> produced a number of internal compiler errors

Up until now it has worked ok for me, but I have mostly used rather
basic concepts and only mild "specialization" of concepts.

> (and I have not found the error messages to be helpful in general). 

True, but that's something where clang had to lead the way before, too,
or not? :)

> Some cases of those internal
> compiler errors stem from the cases being underspecified in the TS.
>

Haven't had any of those because of concepts, yet.

> I am not sure an ETA makes sense if the shape of what is going to be
> delivered is changing. For example, the TS has a one-size-fits-all
> normalization process which can be overly eager; part of the Clang
> implementation effort would be to implement (in consultation with the
> committee) the intended behaviour for each of the uses of normalization.

TBH honest I have no real clue of the scope of implementing the TS fully
in Clang (or what the current progress is) so I am not *suggesting*
anything, but maybe if there was a preliminary usable release in Clang
it would get in more testers and help diagnose issues and corner cases?
I thought this was what the committee wanted and why so many things
didn't make it into C++17, i.e. getting people to use TSes early so that
issues can be found and solved before integration into the proper
standard...
Then again, maybe you already know the rough edges well and would rather
figure them out first?

Thanks for the info and of course for working on this,
Hannes

> 
> On Thu, Feb 9, 2017 at 3:17 PM, Hannes Hauswedell <h2+lists2017 at fsfe.org>
> wrote:
> 
>> Hi Hubert,
>>
>> thanks for the reply and the "warning sign". I am aware that the
>> discussion on Concepts is ongoing, but there is the published ISO/IEC TS
>> 19217:2015 that GCC implements and it has been rather stable from my
>> knowledge.
>> In any case my original question still remains: is there an ETA for
>> concepts in Clang? Is there a person responsible for it right now that
>> could have more details?
>>
>> Thanks,
>> Hannes
>> --
>> pgp-key: https://hannes.hauswedell.net/hannes_hauswedell_public_key.asc
>> fingerprint: FC35 7547 7916 DA55 DC42 27EA 1D57 8E18 A109 60BF
>>
>> On 05.02.2017 18:57, Hubert Tong wrote:
>>> The Concepts TS implementation for Clang is occurring on trunk; so you
>> are
>>> looking in the right place.
>>> Regardless of the implementation status in Clang, the TS remains an
>>> experimental design, which may be subject to change.
>>> So, I think that using relying on the Concepts TS in production carries
>>> some risks: even if the support is there, it might not be the same as GCC
>>> or the current version of the TS.
>>>
>>> -- HT
>>>
>>> On Sun, Feb 5, 2017 at 8:43 AM, Hannes Hauswedell via cfe-dev <
>>> cfe-dev at lists.llvm.org> wrote:
>>>
>>>> Hi everyone,
>>>>
>>>> I wanted to ask what the current state of the Concepts TS is in Clang. I
>>>> saw some older list threads last year, but also didn't see much in
>>>> regard of commits, but maybe I am also looking in the wrong places.
>>>>
>>>> The status page lists it as WIP, but from my own experience I know that
>>>> WIP can me anything from "we are running the last tests before release"
>>>> to "I have put it on the TODO list".
>>>>
>>>> The background is that we are currently redesigning a large template
>>>> library and would really like to make use of concepts. Working with GCC
>>>> during development is not a problem, but when we start distributing
>>>> first release candidates maybe a year from now, it would be important to
>>>> have Clang support, too.
>>>>
>>>> If someone could shed light on the current status and whether there is
>>>> an ETA that would help us a lot. Note that I am not implying that anyone
>>>> should do anything for us, it's just important for us to know whether
>>>> it's something we can likely expect for e.g. clang-6 or "definetely not
>>>> in the next two years".
>>>>
>>>> Thank you,
>>>> Hannes
>>>> --
>>>> pgp-key: https://hannes.hauswedell.net/hannes_hauswedell_public_key.asc
>>>> fingerprint: FC35 7547 7916 DA55 DC42 27EA 1D57 8E18 A109 60BF
>>>>
>>>>
>>>> _______________________________________________
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>>>> cfe-dev at lists.llvm.org
>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>>
>>>>
>>>
>>
>>
>>
> 

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