[cfe-dev] Objective-C++11 literal types

[Richard Smith]

On Fri, December 2, 2011 04:09, John McCall wrote:
> On Dec 1, 2011, at 4:23 PM, Richard Smith wrote:
>> I was surprised to find this in AST::Type::isLiteralType:
>>
>>
>> // Objective-C lifetime types are not literal types.
>> if (BaseTy->isObjCRetainableType()) return false;
>>
>> This is strange, because we do support constant expression evaluation of
>> Objective-C lifetime types (outside C++11).
>>
>>
>> So which is correct? Should lifetime types be permitted as literal types,
>> or should they not be permitted as the type of globals in (Objective-)C? Or
>> is there some reason why C++11 should treat them differently from other
>> languages?
>
> I don't know the reasoning for that change, but I would assume it's
> supposed to apply to ownership-qualified types under ARC, i.e. types with a
> non-trivial ObjCLifetime qualifier, because such types generally require extra
> operations which need to be performed at runtime.  However, I don't know that
> that's actually correct, because any object of such a type that can be
> constant-evaluated must also be statically allocated, which means that retains
> and releases can be completely ignored.  That might be a lot of complexity to
> get right, though.

We allow these types to be subject to constant initialization in (Objective-)
C and C++98 already. If there is extra complexity, handling it in a
C++11-specific fashion seems wrong unless the complexity is C++11-specific --
which I don't think it is. Any objection to my removing this check?

Richard