The contracts syntax is intentionally “attribute-like” but “not actually an attribute”, which allows a compiler to treat those differently.

But the syntax difference is very subtle and a different that a compiler that does not support attributes would be unlikely to check for.

As an example:

  [[something x]]
  [[something(x)]]

The first is an invalid attribute but we could potentially decide to make it a contract, while the second is a valid attribute.

So, C++ is saying that the syntax of the stuff inside “[[ ]]” matters in the contract vs. attribute decision.

I believe that is intentional so that older C++ compilers that support attribute but not contracts will probably ignore them.

I think that also means that unless a C compiler does syntax checking on unrecognized attributes, there should not be an issue.

All of that said, making progress on contracts is an important and also difficult process, and I don’t want to have to guess which other groups might have concerns about our direction.

So, if SG21’s work is of concern to SG22, please make sure that someone is monitoring and or attending our meetings.

Thanks,

John.

> On Sep 20, 2021, at 10:12 AM, Aaron Ballman <aaron_at_[hidden]> wrote:
>
> On Mon, Sep 20, 2021 at 9:54 AM John Spicer via SG21
> <sg21_at_[hidden]> wrote:
>>
>> My personal opinion is that there are SG22 people involved in SG21 and the should bring forward their concerns they might have.
>
> FWIW, I raised some concerns I had when we were early in the process
> of discovering people's concerns. I've since had to step back from
> SG21 participation and haven't been able to follow along, but P1995
> did not give me much hope.
>
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1995r0.html#cdev.ignorable
> As a C Developer
> In order to Write contracts on my functions
> I want to Make all contract semantics optional (so as not to change
> WG14-N2385 6.7.11 p2)
>
> Must Have: 3, Nice to Have: 3, Not Important: 23 , No Answer: 1
>
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1995r0.html#cdev.contracts
> As a C Developer
> In order to Write contracts on my functions
> I want to Specify contracts in a way standardizable as part of the C language
>
> Must Have: 2, Nice to Have: 6, Not Important: 21 , No Answer: 1
>
> It seems to me like there's a reason for SG22 to be involved given
> that C has the same [[]] syntax that C++ has and likely has opinions
> on designs in that space that are incompatible with their
> expectations.
>
>> The authors have already been working on wording.
>>
>> IMO, the SG22 impact is not any greater than it was for the C++20 contracts proposal, so if they didn’t have problems with that, they shouldn’t have concerns now.
>
> SG22 was formed after C++20, so there was no official study group
> stance on the proposal at that time. However, compatibility with C was
> one of the reasons I voted strongly against contracts in C++20 and
> helped push me to form SG22 in the first place. My (admittedly fast
> and not thorough) reading of P2388R0 has the same concerns as before.
> I think getting the SG22 perspective would be useful in hopefully
> avoiding future NB comments, especially because those can arrive
> through other committees than WG21.
>
> ~Aaron
>
>>
>> John.
>>
>>> On Sep 20, 2021, at 9:18 AM, Peter Brett <pbrett_at_[hidden]> wrote:
>>>
>>> Hi all,
>>>
>>> Please at least get outline approval from SG22 for the syntax before proceeding to spend time writing wording.
>>>
>>> Best regards,
>>>
>>> Peter
>>>
>>>> -----Original Message-----
>>>> From: SG21 <sg21-bounces_at_[hidden]> On Behalf Of John Spicer via SG21
>>>> Sent: 13 September 2021 11:06
>>>> To: SG21 - Contracts <sg21_at_[hidden]>
>>>> Cc: John Spicer <jhs_at_[hidden]>
>>>> Subject: [isocpp-sg21] Telecon to review P2388R1 Minimum Contract Support:
>>>> either Ignore or Check_and_abort
>>>>
>>>> EXTERNAL MAIL
>>>>
>>>>
>>>> We’d like to have a telecon to discuss this paper.
>>>>
>>>> We are thinking about either Tuesday 9/21, 9/28, or 10/5 at 8 AM Pacific
>>>> time.
>>>>
>>>> Please indicate your preference at this Doodle page:
>>>>
>>>> https://urldefense.com/v3/__https://doodle.com/meeting/participate/id/mbkZ7Z
>>>> 6a__;!!EHscmS1ygiU1lA!S7mTfbNuJm-ECRyonHAxUX-
>>>> WCICkzN9Bo8PvtmHnnslnt0YaN8QUMTi3OMtKqw$
>>>>
>>>> Thanks,
>>>>
>>>> John Spicer
>>>> SG21 Contracts Chair
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