Is init() needed in Objective C

Question

I am new to Objective C. I have trouble with understanding the init() method. I have read these two lines on Apple website:

1. The init() method defined in the NSObject class does no initialization; it simply returns self. (https://developer.apple.com/reference/objectivec/nsobject/1418641-init)

2. You must use an init... method to complete the initialization process. (https://developer.apple.com/reference/objectivec/nsobject/1571958-alloc)

Do I need to call init() to initialize objects if "it does no initialization"? Why?

Answer 1

When an instance object is created with +alloc, it gets a fully set-up infrastructure and all ivars are set to 0, NULL, nil, 0.0 (or whatever ist the zero value for the ivar's type).

If this is enough for the class, there is no need to overwrite -init and it can simply use NSObjects init. (-init of NSObject simply does nothing.) This is the implementor's side. This is what you refer to at 1).

The user of the class (that code, that created the instance), has to send init to the newly created instance to give it the opportunity to initialize itself. This is what you refer to at 2).

As a user of the class, you simply cannot know and should not know, whether the class requires some code in its initialization process. So send the message, even if it might be useless.

Answer 2

From Apple Developer on Object Initialization :

If an object does not implement an initializer, Cocoa invokes the initializer of the nearest ancestor instead.

Yes, you need to call some form of init to create your object on the heap. The init returns a point to the memory location. No, you don't need to write an init for your custom object unless the default set-everything-to-zero initialization is insufficient.