Understanding what I'm doing...

[nexus]

Hi all,

I'm getting into Objective-C and I'm beginning to understand the concepts of OOP.

I'm trying to figure out what and idea of what is going on here:

- (id) init
{	
	self = [super init];
	
	if (self)
	{
		value = 0.0;
		for (int i = 0; i < 6; ++i)
			savedValues[i] = 0.0;
	}

	return self;
}

Mainly the self [super init] line is what I'm trying to understand.

Any help would be appreciated.

[ZunePod]

The second block of code is initiating the viewcontroller and setting some values.

[Mr Jack]

Originally Posted by nexus

Mainly the self [super init] line is what I'm trying to understand.

In objective-C the keyword super is a pointer to the class inherited from. This allows you explicitly call functions in the base class (aka superclass) that you've overridden in your derived class (aka sub class).

So, [super init] calls the init function on the class you're inheriting from, which probably calls it on the class inherits from and so on up the chain, ensuring that every "layer" of the inheritance hierarchy gets initialised properly.

[smasher]

In general, classes "extend" or "inherit from" other classes. That means they perform all the functions of the "parent" class, also called a "super class" , plus whatever functions you add.

If you check the your .h file, you'll see that your class extends some other class, probably NSobject.

@interface MyClass : NSObject

The superclass usually performs important setup in its init method, you you had better call it using [super init] if you want it to be run when your init is called.

In the same vein, if someone ever subclasses your class you want to make sure they run your init method, right? So they call [super init] which runs your init method which calls [super init] which runs NSObject's init method. That's the chain Mr Jack mentioned.

Extra credit:
The reason you say self=[super init] is that for some classes "init" can return a different address than the one it was called on. This only happens in specialized cases like singletons, but you should code for it anyway.

[nexus]

Thanks guys for the responses. A little over my head right now, but I'll learn...