Implement a pure virtual method in Objective-C

Question

I want to go to there. Seriously though, how does one implement a pure virtual method in an \"Apple\" way? Do you use a Protocol with your base class and throw exceptions on

Answer 1

You have a few options, but you're on the right track.

ObjC doesn't support this directly, forcing subclasses to implement a protocol is the best way to check it at compilation.

'Secretly' implementing the method in the base class and asserting is what I do to confirm the subclasser has subclassed correctly at runtime. Some people have mixed feelings about assertions, or must leave them active, so that's not always a good solution.

You can also force subclasses use a specific class constructor and initialization sequence, then verify they have implemented everything required before returning an instance, in case compiler warnings don't cut it.

But ObjC is missing some lang features which allow clients to shoot themselves in the foot, or workaround what they wish so... you shouldn't get too stuck on enforcing it.

note: Exceptions are very uncommon (and a bit unsafe, too) in ObjC.