Question

If assign is a setter, but a property is readonly, then it will not be doing any setting, so why use assign ?

I am getting this from the Apple docs on class extensions. In this page, I get why you’d want a public readonly property, then make it privately readwrite, but then why not omit the assign from the public @interface and just include it in the class extension only?

Answer 1

If you declare a @property multiple times (typically because you declare a public readonly property in the header file, and a readwrite property in an anonymous category in your .m), the memory management schemes have to match.

So if you have this in your .m:

@property (assign, readwrite) NSObject *foo;

Then you need this in your header, and the assign is mandatory:

@property (assign, readonly) NSObject *foo;