I'm new at this too, so perhaps I am completely off here. My guess is that it
isn't the const that is messing this up, but the non-class type. The problem I
see is that "frame" is a pointer to an objc_object and objc_objects aren't the
same as NSObjects (but, like I said, I'm new, so maybe they are interchangeable
here). Does it work if you try declaring frame as a NSObject<FrameProtocol>
instead of an id<FrameProtocol>?
Aaron
On Nov 8, 2010, at 8:37 AM, Jonny Taylor wrote:
> I'm afraid I'm not sure if I understand exactly what you're asking. I would
> like to be able access the "frame number" property (which is in fact stored
> as a variable within the class, and is fixed soon after instantiation) in
> spite of the fact that I only have a 'const' pointer to the object at the
> time I want to access it. Semantically I don't see why it should be unsafe to
> attempt to find out the value of that property.
>
> Either way, hopefully the actual code helps to answer your question:
>
> -(void)analyzeFrameAsync:(id<FrameProtocol>)frame
> {
> int num = frame.frameNumber; // Temporary variable avoid
> problems with calling method on 'frame' [const] from block
> dispatch_async(analysisSerialQueue,
> ^{
> [analyzer processFrame:frame];
> self.latestFrameNumberProcessed = num; // I can't call
> frame.frameNumber from within the block (compiler error)
> });
> }
>
>
>
> On 8 Nov 2010, at 16:29, David Duncan wrote:
>
>> It might be useful to know what you expect to get from the const reference
>> in the first place? Primarily because I highly suspect that it is not
>> necessary to ensure the semantics that you desire.
>>
>> On Nov 8, 2010, at 4:59 AM, Jonny Taylor wrote:
>>
>>> I have encountered what I presume is a common newcomer's problem, but I
>>> haven't had any luck with google (maybe I'm using the wrong search terms?).
>>> Suppose I have a const id, e.g. "const id<FrameProtocol> frame". If I
>>> attempt to call a getter for the object I get the following compiler error:
>>> request for member 'frameNumber' in 'frame', which is of non-class type
>>> 'objc_object* const'
>>
>> --
>> David Duncan
>>
>
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