Objective-c: Questions about self = [super init]

Question

I have seen self = [super init] in init methods. I don\'t understand why. Wouldn\'t [super init] return the superclass? And if we point

Answer 1

As you have Question self = [super init] in the if Condition suggest a specific meaning.

First of all [super init] gives the initialization of the superclass of the existing class which is in use currently. Using [super init] gives the super class initialization which shows that object exist of the class.

Now when you use self = [super init] that means you are assigning the class to the self for the further utilization of the same class.

And at the end you put it in if condition as if(self = [super init]) this means you are checking whether the object of the class exist of not to prevent the foul behavior of the application.

I think it is clear now!!!

Answer 2

I would think of it as, init'ing all the supers variables etc, then you get to init your extended classes variables before it is returned.

Answer 3

Self = [super init];

According to JAVA, this mean a pointer to instance itself so object can message itself.

Same meainng of Self here in objective C,

According to JAVA, Super mean that allow to access base or parent class

Same meainng of Super here in objective C,

Now init instance to to complete the initialization process.

Answer 4

Every method that you declare has two hidden parameters: self and _cmd.

The following method:

- (id)initWithString:(NSString *)aString;

is converted by the compiler to the following function call:

id initWithString(id self, SEL _cmd, NSString *aString);

see this link for more:

http://www.cocoawithlove.com/2009/04/what-does-it-mean-when-you-assign-super.html

Answer 5

[super init] is the same as [self superclass_variant_of_init]

If you want to send a message to superclass, there is another approach (without using runtime library):

[[self superclass] init];

Answer 6

@MartinR has a very good answer. But do you ever wonder why "[super init] calls the superclass implementation of init with the same (hidden) self argument. (This might be the point that you understood wrongly.)" works in his 3rd point ?

Here is the excerpt from Big Nerd Ranch guide 3rd edition, chapter 2 Objective C that clarifies this point

“How does super work? Usually when you send a message to an object, the search for a method of that name starts in the object’s class. If there is no such method, the search continues in the superclass of the object. The search will continue up the inheritance hierarchy until a suitable method is found. (If it gets to the top of the hierarchy and no method is found, an exception is thrown.)”

“When you send a message to super, you are sending a message to self, but the search for the method skips the object’s class and starts at the superclass.”

This code shows how iOS Runtime performs this task

objc_msgSendSuper(self, @selector(init));