Question

I stumbled upon this post In Objective-C why should I check if self = [super init] is not nil?

I can understand this syntax:

- (id)initWithString:(NSString *)aString
{
    self = [super init];
    if (self)
    {
        instanceString = [aString retain];
    }
    return self;
}

or this syntax:

- (id)init;
{
 if (!(self = [super init]))
   return nil;

 // other stuff
 return self;
}

but I still don’t understand the “standard” template syntax

- init {
    if((self = [super init])) {
        // set up instance variables and whatever else here
    }
    return self;
}

Can someone tell as clearly as possible what (3) does more or less compared to (1) or (2) ? All I read is so confusing (why people can’t agree with something which is purely technical seems like politics :))

Nevertheless as I read authors article, and as I can fuzzily understand it goes far beyond just syntactic sugar debate or matter of taste. For example it is said:

Curiously then, while case 3 is overwhelmingly more common, initializers that support 1, 2 and 4 but are incompatible with case 3 have become the standard.Curiously then, while case 3 is overwhelmingly more common, initializers that support 1, 2 and 4 but are incompatible with case 3 have become the standard.

So I’d like to have a deep philosophical answer from Objective C Gurus if possible.

Answer 1

The key to understanding (3) is the if line

if((self = [super init])) {

In C, every operator has a return value, you just don’t have to use it. So just as 3 + 4 returns 7, the operator = returns the same value that was just assigned. That allows you to do interesting things like this with it:

int a, b, c, d;

a = b = c = d = 5;

(This works because the operator has right-to-left associativity. This means that a = b = 3;is equivalent to a = (b = 3); so b is set to three first, then a is set to that same value.)

So now we can observe that the test

if((self = [super init])) {

is exactly the same as

self = [super init];
if (self) {

They all do exactly the same thing, though. As for the preferred option, a lot of people think that putting expressions into if statements is bad practice, as it’s hard to notice if you’re not used to it. Apple do seem to have settled with the first example you listed in their templates, and have also added a compiler warning for the first, if you try to do it without the stupid double brackets if(()).