C++11 attributes for C11 (was Re: [PATCH] Generalized attribute support)

[Nico Weber]

On Sat, Apr 19, 2014 at 4:05 PM, Alp Toker <alp at nuanti.com> wrote:

> Small update for the list..
>
> We discussed this at LLVM Europe 2014 and came to the conclusion that we
> might as well offer the feature behind an -f flag.
>
> This should satisfy user requests for C++11-style attributes in C11
> without prejudicing any standards process. Thanks to the many detailed
> use-cases people sent in that have made me more comfortable picking this up
> again.
>

Are these use-cases visible anywhere?


>
> So, I've got a slightly improved version of the patch and will aim to
> rebase and post it to the list for review in the coming weeks.
>
> All we need now is great name for the -f flag ;-)
>
> Alp.
>
>
> On 15/01/2014 20:44, Alp Toker wrote:
>
>>
>> On 15/01/2014 20:29, Richard Smith wrote:
>>
>>> On Wed Jan 15 2014 at 3:42:08 AM, Alp Toker <alp at nuanti.com <mailto:
>>> alp at nuanti.com>> wrote:
>>>
>>>
>>>     On 15/01/2014 06:04, Nico Weber wrote:
>>>     > Does gcc allow this for C? Is C planning on standardizing this?
>>>
>>>     The impression I get is that everybody's doing it but nobody's
>>> talking
>>>     about it. Yet.
>>>
>>>
>>> Weird. The impression I get is that nobody is doing it (at least, not
>>> publically).
>>>
>>
>> People said they were patching internally to use new security and
>> optimization attributes, and presumably there are others ("nobody's talking
>> about it"). Seems a reasonable use case.
>>
>>
>>> What if a future revision of a standard we care about (maybe C, OpenMP,
>>> OpenCL, CUDA, ...) standardizes a *different* meaning for square brackets?
>>> Code that used our extension would be in trouble.
>>>
>>
>> This is a great reason to hold back from switching it on globally.
>>
>> If we don't have "nudge" power in getting this as a de-facto C1y feature
>> it becomes less interesting.
>>
>>
>>> This isn't even purely theoretical -- Objective-C does this, and it is
>>> essentially only by luck that it's possible to disambiguate this fully. As
>>> another example, if C17 took C++'s lambdas but not its attributes, we'd run
>>> into some amount of trouble with expressions like
>>>
>>>  int x[ [] { ... } () ];
>>>
>>> (which is an ill-formed attribute under the C++11 rules).
>>>
>>
>> It'd be far from the worst disambiguation we have in-tree.
>>
>> Objective-C disambiguation is working fine with the C11 extension enabled
>> for what it's worth.
>>
>> I'm withdrawing the patch, there are probably more useful things to be
>> working on.
>>
>> Tentatively setting a date to revisit this in a years time or after gcc
>> implements, whichever comes first, when there might be a clearer way
>> forward.
>>
>> Alp.
>>
>>
>>
> --
> http://www.nuanti.com
> the browser experts
>
>
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