Clang 3.1: interesting warning...

gistfile1.m

@protocol MyProtocol <NSObject>

@end

int main(int argc, char *argv[])
{
    @autoreleasepool
    {
        id <MyProtocol> foo = nil;
        __unused id value = [foo valueForKey:@"bar"];
        
        return EXIT_SUCCESS;
    }
}

The protocol that I have wrote does not declare valueForKey:, but this method should still be accessible through the category NSKeyValueCoding on NSObject. The following code does not generate warning:

id foo = nil;
id value = [foo valueForKey:@"bar"];

This one does:

id < MyProtocol > foo = nil;
id value = [foo valueForKey:@"bar"];

It is as if the compiler does not consider the type 'id < MyProtocol >' of type 'id'. Which is really odd. And so if you force the cast of foo into an id, the code compile without any warning.

id < MyProtocol > foo = nil;
id value = [(id)foo valueForKey:@"bar"];

I understood :) http://unixjunkie.blogspot.com/2008/03/id-vs-nsobject-vs-id.html