Program 3.2 - need to assign results of [myFraction init]?

[John Dallman]

Program 3.2 has (with comments I added):

Code: (Objective-C)

Fraction *myFraction;                  // Note not initialised yet.
myFraction = [Fraction alloc];        // Allocate memory - inherited
myFraction = [myFraction init];      // Initialise - inherited

I understand [Fraction alloc], which allocates memory and returns a pointer to the object. That's clear. [myFraction init] initialises the object, which may not do anything in this example, but will be required for many real-world objects.

But I'm a bit puzzled by the need to assign the result of [myFraction init] to myFraction. The object already has an address, and putting in a few NSLog calls reveals that the pointer in myFraction has the same value before and after the [myFraction init] call. I can immagine scenarios where that might be necessary, but they don't seem very plausible.

Is this actually a useful convention?

[John Dallman]

And now I've read a bit further, I see where it comes from: it's a natural result of being used to writing [[Class alloc] init], and then breaking it up to be less intimidating-looking.

[[I code:forFun]]

I wonder if it could be that when you initialize the 'myFraction' object, it is stored in a new place in memory, and thus you would want to assign that newly returned address to the 'myFraction' variable.  Or maybe it is the same address, and I'm missing something else important.  Hopefully someone will chime in that knows for sure.   : )

The book says: alloc returns the address in memory of the newly created object, and init returns the initialized object.  So I think my first guess is wrong.  Still want an explanation too.