What happens to alloc if initWithX fails?

Question

It is common practice to write MyClass* obj = [[MyClass alloc] initWithX:X] in Objective-C. initWithX is usually defined as

- (MyClass*) initWithX: (MyArgClass*) X {
    if (self = [super init])  {
        // initialize
    }
    return self;
} 

My question is: what if initialize fails? I don't want to throw exceptions, but, how do I indicate error? If I return nil, the caller will not be able to release the pointer.

Answer 1

If initialization fails for any reason you should release self. For an exception that may occur in your initialization you need to add you @try @catch as appropriate so you can release self.

- (MyClass*) initWithX: (MyArgClass*) X {
    if (self = [super init])  {
        // initialize
        if(myInitializationCodeFailed)
        {
                [self release];
                return nil;
        }
    }
    return self;
}

Update

If it is possible for your initialization fail I would not raise an exception from with in your initialization code. If you would like to provide the caller with information I would refactor the initializer to accept an NSError to be returned.

- (MyClass*) initWithX: (MyArgClass*) X error:(NSError**)error {

As Alexei Sholik points in the comments check out the Handling Initialization Failure section of Allocating and Initializing Objects.