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Editorial Team
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Asked: 2026-05-11T21:15:49+00:00

In Java, it is very easy to code the following design: public abstract class

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In Java, it is very easy to code the following design:

public abstract class Pizza {
    public static final Pizza.NULL = new Pizza() {
        /* "null" implementations */
    }

    /* actual/abstract implmentations */
}

What is the preferred method to attain the same efficient scenario in Objective-C? I have been unable to find any documentation on the subject, and I have tried a couple different scenarios with static const, #define etc. but none of them seem to work out as well as the Java method above.

I would like to avoid writing a concrete NullPizza class that has a static method to obtain the singleton instance, as it seems more ‘proper’ for it to be some final property/field of the highest-level interface. (Pizza, in this case.)

Edit: While I understand how the NULL pattern specifically would be handled due to Obj-C’s unique method of handling method calls to ‘nil’, what about other static common instances, such as Response.YES and Response.NO? (See comments for discussion.)

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1 Answer

  1. Editorial Team

    For your Response.YES and Response.NO, I assume you have instances that you do want to change, rather than just making all Response properties read-only.

    A common pattern in Cocoa is to have both immutable and mutable versions of a class (NSArray versus NSMutableArray). For your response example, it would make sense to have an immutable Response class that has the static YES and NO methods, and a MutableResponse subclass that exposes setters for those times where you do want objects to change them. Does this cover your second example?

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