objective c - Does @property copy in combination with readonly make sense?

Question

If I understand this correctly, copy enforces the setter to create a copy of the object passed in. However, if I use it together with readonly, there won't be a setter. So is my assumption correct, that combining @property (copy, readonly) doesn't make any sense or am I missing something?

Answer 1

It does make sense. For instance, if you want to access a property's setter in your implementation only:

@interface MyClass : NSObject
@property (nonatomic, copy, readonly) NSData *data;

- (id)initWithData:(NSData *)data;

@end

and in the class continuation in the .m file:

@interface MyClass ()
@property (nonatomic, copy, readwrite) NSData *data;
@end

Note that the copy, readonly declaration in the public header is required in this case!