Chapter 10 - initialize self using super

[seerex]

Hello fellow objective-c apprentices

I just started reading chapter 10, and the first example of a code i stumble upon is the one where you create a Fraction method that initializes and sets the instance of a Fraction. I have a question though.

You create this method

Code: (Objective-C)

-(Fraction *) initWith: (int) n: (int) d {
    self = [super init];
    
    if (self)
        [self setTo: n over: d];
    
    return self;
}

And according to my understandings what it does is that it initializes the parent class(s) and assigns em to self, hence self gets initialized aswell.

After that if it returns a non-zero value meaning the initialization was completed properly, it sets the instance variables of self.

And then returns self.

I have 2 questions regarding this matter.
1. "self" is the message caller / invoker, right? and when using a = [method] a is the one getting the received Fraction object hence of the return of a Fraction object, correct?

2. The book gets you to write this code

Code: (Objective-C)

b = [[Fraction alloc] initWith: 3 : 7];

From my point of view, it simple calls 2 methods right? the inherited alloc method and the newly created init method that sets the values of numerator and denominator. So this is actually 2 methods combined on 1 line, correct? hence the same result would apply if you did

Code: (Objective-C)

b = [Fraction alloc];
b = [initWith: 3 : 7];

Although it does not? and since the initWith is just a plain method like the print and others, why doesnt this apply? i'm assuming it must have something to do with it being initialized and you cant use methods if it isn't initialized, however, thats what you do here before it assigns the values, correct?

and to get a bit more confusing, but i guess this question is answer simultaneously with the above, but i also tried doing this

Code: (Objective-C)

a = [[[Fraction alloc] initWith: 1 : 3]printAndConvert];

obviously doesnt work either

It is properly explained in the book and maybe i just missed it or simply forgot it, coz english isnt my native language and on top of that its my very first programming language so im struggling both to learn and also to read and understand some of the more "complex" sentences.

Thank you for taking your time to read this long and tedious post, but your effort in helping me out is greatly appreciated.

Best regards

[skochan]

The two line version would look like this:

Code: (Objective-C)

b = [Fraction alloc];  
b = [b  initWith: 3 : 7];  

since you want to take the result of the alloc and send it the initWith:: message.

For the second case, you don't return a value from your printAndConvert method, so you would write

Code: (Objective-C)

 [[[Fraction alloc] initWith: 1 : 3]printAndConvert];  

Hope this helps.  Note that this example has a memory leak since you don't save the reference to the allocated Fraction object and therefore can't release it.

 Cheers,

Steve

[seerex]

Evening sir.

Thanks a lot, it clears it up i'll get my head back in the book when i'm done i'll order the third edition so i cant wait. Really good book and great forum!

best regards