NSArray @property backed by a NSMutableArray

Question

I've defined a class where I'd like a public property to appear as though it is backed by an NSArray. That is simple enough, but in my case the actual backing ivar is an NSMutableArray:

@interface Foo
{
    NSMutableArray* array;
}
@property (nonatomic, retain) NSArray* array;

@end

In my implementation file (*.m) I @synthesize the property but I immediately run into warnings because using self.words is the same as trying to modifying an NSArray.

What is the correct way to do this?

Thanks!

Answer 1

I would declare a readonly NSArray in your header and override the getter for that array to return a copy of a private NSMutableArray declared in your implementation. Consider the following.

Foo.h

@interface Foo

@property (nonatomic, retain, readonly) NSArray *array;

@end

Foo.m

@interface Foo ()

@property (nonatomic, retain) NSMutableArray *mutableArray

@end

#pragma mark -

@implementation Foo

@synthesize mutableArray;

- (NSArray *)array
{
    return [[self.mutableArray copy] autorelease];
}

@end