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

Alp Toker alp at nuanti.com
Sat Apr 19 16:05:38 PDT 2014

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.

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 ;-)


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.

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