Question

I am having problems understanding what/how this works. it seems odd assigning self to return from the init message

- (id)init
{
    if((self=[super init])) {
       //code here for setting up
    }

    return self;    
}

Answer 1

The init method first assigns the implicit self local variable (self is one of the two hidden arguments passed to methods) to the return value of the superclass’s designated initializer. The reason behind this is that initializers can return a different object than the one that received the message, for example, when it is not possible to initialize the receiver correctly or when an existing instance is returned to avoid the need to initialize a new one.

After self is set, the if statement ensures that instance variables are only initialized if self is not nil. If self is nil, accessing the memory for the instance variables may be an error. Very few classes return nil but still it is a valid return value.

This is described in Implementing an Initializer.