Sparse Array - FoundationAdditions

NSArray+FoundationAdditions.m

@implementation NSArray (FoundationAdditions)

-(id) objectAtCheckedIndex:(NSUInteger) index {
	if(index >= self.count) {
		return nil;
	} else {
		id result =  [self objectAtIndex:index];
		return result == [NSNull null] ? nil : result;
	}
}

@end

NSMutableArray+FoundationAdditions.m

@implementation NSMutableArray (FoundationAdditions)

-(void) setObject:(id) object atCheckedIndex:(NSUInteger) index {
	NSNull* null = [NSNull null];
	if (!object) {
		object = null;
	}
	
	NSUInteger count = self.count;
	if (index < count) {
		[self replaceObjectAtIndex:index withObject:object];
	} else {
		if (index > count) {
			NSUInteger delta = index - count;
			for (NSUInteger i=0; i<delta;i++) {
				[self addObject:null];
			}
		}
		[self addObject:object];
	}
}

@end