How to declare an immutable property backed by a mutable type?

Question

I’d like to declare a public immutable property:

@interface Foo
@property(strong, readonly) NSSet *items;
@end

…backed with a mutable type

Answer 1

You have to declare the property in the public interface as readonly in order the compiler not to complain. Like this:

Word.h

#import 

@interface Word : NSObject
@property (nonatomic, strong, readonly) NSArray *tags;
@end

Word.m

#import "Word.h"

@interface Word()
@property (nonatomic, strong) NSMutableArray *tags;
@end

@implementation Word
@end