Thankyou everybody for your help (and patience!) with this one. I have indeed
been making some wrong assumptions and as I result much of what I was writing
was incorrect. From the various helpful replies I have received, I have (I
hope!) got a much clearer understanding of what is and isn't going on.
I now think that what I am seeing is a minor parsing sort of issue within the
compiler (gcc 4.2) when mixing id<SomeProtocol> with blocks. In the example
code below, everything works ok except for two lines, which lead to compile
errors. [The mention of 'const' in the error was what was leading to my
incorrect claims earlier, since that had got me thinking the problem was
related to how you can't by default modify variables declared outside blocks.
Sorry!].
I believe the compiler should not be objecting to the lines that it reports
errors for...
Jonny
===== BEGIN CODE =====
// Declare a class with a property
@interface MyClass
@property (readwrite) int frameNumber;
-(int)frameNumber2; // Try declaring a straight function
just to see if it makes a difference
@end
void foo(MyClass *m)
{
printf("%d %d n", m.frameNumber, m.frameNumber2); // ok
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),
^{
printf("%d %d\n", m.frameNumber, m.frameNumber2); // ok
});
}
// Try the same, but with a protocol rather than a concrete class type
@protocol MyProtocol
@property (readwrite) int frameNumber;
-(int)frameNumber2;
@end
void foo2(id<MyProtocol> m)
{
printf("%d %d n", m.frameNumber, m.frameNumber2); // ok
printf("%d %d\n", [m frameNumber], [m frameNumber2]); // ok
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),
^{
// Both these have errors: "request for member 'frameNumber' in
'm', which is of non-class type 'objc_object* const'"
// when compiled as ObjC++ (.mm file).
// I get a different error: "request for member 'frameNumber'
in something not a structure or union"
// when compiled as ObjC (.m file).
printf("%d\n", m.frameNumber);
printf("%d\n", m.frameNumber2);
// Both these are ok
printf("%d %d\n", [m frameNumber], [m frameNumber2]);
});
}
===== END CODE =====
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