Can I setup the tires array below as an NSArray?

Question

I have looked on the web but can't find anything that might help. My question is can I write the tires[x] array as an NSArray, if so what would be the syntax to both declare and allocate the tire Class instance objects?

@interface CarClass : NSObject {
    EngineClass *engine;
    TireClass *tires[4];  
}

.

@implementation CarClass
- (id) init {
    [super init];
    NSLog(@"_init: %@", NSStringFromClass([self class]));
    engine= [[EngineClass alloc] init];
    tires[0]= [[TireClass alloc] init];
    tires[1]= [[TireClass alloc] init];
    tires[2]= [[TireClass alloc] init];
    tires[3]= [[TireClass alloc] init];
    return self;
}

EDIT:

this is my dealloc method for the CarClass

- (void) dealloc {
    NSLog(@"_deal: %@", NSStringFromClass([self class]));
    [engine release];
    [tires release];
    [super dealloc];
}

Still a bit confused about the retain in the NSArray below, if I add an extra [tires retain] to the CarClass:init then the tires do not get released. However as the code is now the tires release with or without the end retain (i.e.)

tires = [[NSArray arrayWithObjects:
        [[[TireClass alloc] init] autorelease],
        [[[TireClass alloc] init] autorelease],
        [[[TireClass alloc] init] autorelease],
        [[[TireClass alloc] init] autorelease],
        nil] retain];

tires = [NSArray arrayWithObjects:
        [[[TireClass alloc] init] autorelease],
        [[[TireClass alloc] init] autorelease],
        [[[TireClass alloc] init] autorelease],
        [[[TireClass alloc] init] autorelease],
        nil];

FINAL EDIT: I also thought that without the autorelease on the individual tires that finally releasing the NSArray in the dealloc would release both the array and the objects it points to, this does not seem to be the case.

cheers -gary-

Answer 1

@interface CarClass : NSObject {
    EngineClass *engine;
    NSArray *tires;
}

.

@implementation CarClass
- (id) init {
    self = [super init];
    if (self == nil)
        return nil;
    NSLog(@"_init: %@", NSStringFromClass([self class]));
    engine= [[EngineClass alloc] init];
    tires = [[NSArray arrayWithObjects:
        [[[TireClass alloc] init] autorelease],
        [[[TireClass alloc] init] autorelease],
        [[[TireClass alloc] init] autorelease],
        [[[TireClass alloc] init] autorelease],
        nil] retain];
    return self;
}

Answer 2

You don't always need to use an NSArray for collections. How about this way which has a bit more information about each tyre:

@interface CarClass : NSObject {
    EngineClass *engine;
    NSDictionary *tiresDictionary;
}

@implementation CarClass
- (id) init {
    self = [super init];
    if (!self) {
        return nil;
    }
    NSLog(@"_init: %@", NSStringFromClass([self class]));
    engine= [[EngineClass alloc] init];
    tiresDictionary = [[NSDictionary dictionaryWithObjectsAndKeys:
    [[[TireClass alloc] init] autorelease], @"LeftFrontTyre",
    [[[TireClass alloc] init] autorelease], @"RightFrontTyre",
    [[[TireClass alloc] init] autorelease], @"LeftRearTyre",
    [[[TireClass alloc] init] autorelease], @"RightRearTyre",
    nil] retain];
    return self;
}

This way you still have a collection class, but rather than try and remember which index of an array refers to which tyre, you have a dictionary with descriptive keys so you can refer to each tyre by a name.

Answer 3

I would change Nikolai's example a bit. Since I do not want to add autorelease and retain where none is needed, less code is always less bug-prone code.

@interface CarClass : NSObject {
  EngineClass *engine;
  NSArray *tires;
}

@implementation CarClass
- (id) init {
  self = [super init];
  if (self) {
    NSLog(@"_init: %@", NSStringFromClass([self class]));
    engine= [[EngineClass alloc] init];
    tires = [[NSArray alloc] initWithObjects:
        [TireClass new], [TireClass new], [TireClass new], [TireClass new], nil];
    [tires makeObjectsPerormSelector:@selector(release)];
  }
  return self;
}

The [tires makeObjectsPerormSelector:@selector(release)]; can be scary, but is useful and also very performant. A slightly less performant way, but maybe more clear would be to let the TireClass implement a factory method, and create autoreleased objects from that one. Like so:

+(TireClass)tire;
{
  return [[self new] autorelease];
}

Also please stop naming your classes "Something"Class, a kitten dies if you do :)