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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