[cfe-commits] r161362 - in /cfe/trunk: include/clang/Basic/DiagnosticSemaKinds.td lib/Sema/SemaExpr.cpp lib/Sema/SemaExprMember.cpp test/SemaObjC/warn-direct-ivar-access.m

[Douglas Gregor]

On Aug 7, 2012, at 9:43 AM, jahanian <fjahanian at apple.com> wrote:

> 
> On Aug 6, 2012, at 5:42 PM, Jordan Rose wrote:
> 
>> 
>> On Aug 6, 2012, at 17:37 , Fariborz Jahanian <fjahanian at apple.com> wrote:
>> 
>>> 
>>> On Aug 6, 2012, at 5:09 PM, Jordan Rose wrote:
>>> 
>>>> Why does this only warn under non-GC?
>>> 
>>> I don't know. This is an old GCC option and brought it over as-is to clang. I don't have the original gcc radar
>>> to look for the rational. Could be that under GC it is safe to do direct assignment while with the advent of
>>> properties, users warn to catch such accesses and use the property syntax which controls the ivar
>>> access with its own APIs (think atomic vs non-atomic).
>> 
>> The same is true under ARC, though. If this is a safety warning, it only really needs to be on for MRC and __unsafe_unretained ivars. I think it's more often a consistency thing, though: if you want Key-Value Observing to work right you have to use the properties.
>> 
>> As a heuristic, people often access ivars directly in -init methods and in -dealloc, since properties may be overridden by subclasses. If we were going to split the difference on the warnings, it could be on by default everywhere except -init and -dealloc methods.
> 
> My intention was to closely follow gcc's behavior wrt -Wdirect-ivar-access.

There's no point in modeling GCC 4.2's behavior, because it isn't relevant for Objective-C. Wdirect-ivar-access is intended to warn about direct access to ivars in places where one should probably have accessed a property instead. That has nothing to do with GC or ARC, so the warning should not dependent on the (absence of) those features.

	- Doug
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