NSArray @property backed by a NSMutableArray

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