[cfe-dev] Objc, cannot cast 'super' error

Dave Keck davekeck at gmail.com
Sun Jul 3 16:54:02 PDT 2011

Hi David,

> No it isn't.  If you are explicitly sending messages that a class does not respond to then an informal protocol is exactly what you want.

I consider informal protocols as workarounds created before formal
protocols supported @optional methods, which is why I avoided option
3. Am I wrong in that assessment?

> Note that there is nothing stopping you from using both a formal and informal protocol, if you wish for explicit testing.

I ended up doing something close to that; I still have the mentioned
MyProtocol, but also MyCategory on NSObject that implements MyProtocol
as the base case, by simply throwing a custom exception as you
describe. A much cleaner approach indeed, and it gets rid of the

> Using these exceptions is very bad style for several reasons:
> 1) Exceptions in Objective-C are intended to indicate programmer error and are very slow.  Using them for a recoverable error is bad.
> 2) You are overloading the meaning of an exception, making it difficult to distinguish between a real error and this error.
> 3) Code that assumes 1) (i.e. most Cocoa code, including code compiled with ARC enabled) will leak memory if it's in any intervening stack frames.

I consider my use of exceptions to be in-line with what you describe:
some programmer made an error and isn't handling a token as they

Thanks for your insight!


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