I'm trying to subclass NSInputStream, but when I call open on my subclass, the program crashes with the 'open only defined for abstract class' exception. I read the documentation for NSStream which says I need to implement open among other methods, but I'm subclassing NSInputStream which already has a working open method, which would be just fine for me.
What's the reason of the above exception? Is there a language concept that I don't get? Someone please enlighten me.