Why in Objective-C does doing alloc and init in separate statements cause the object to be released according to the Xcode static analyzer?

Question

I\'m making my first steps with Objective-C and have encountered a minor, albeit confusing issue with the static analyzer (Product->Analyze) in XCode 4.1. I have created a

Answer 1

So is it possible that init can return a different pointer than the one passed to it from alloc, rather than just configuring the memory it has been passed?

absolutely.

With this code should I pair [ a release ] with the alloc or [ f release ] with the init?

you would assign the value of the initialized object to f (as you have). at this point, a may be a dangling pointer (if another address is returned). thereore, f should be released.

the explanation for this order is that the object may have opted to return a specialized version/variant of itself, and this reallocation happens along the init... chain.

silly demonstration:

@interface Fraction : NSObject
{
@private
    int numerator;
    int denominator;
}

@end

static Fraction* EvilFraction = ...;

@implementation Fraction

- (id)initWithNumerator:(int)num denominator:(int)den
{
    self = [super init];
    if (nil != self) {
        if (0 == den){
            [self release];
            return [EvilFraction retain];
        }
    }
    return self;
}

@end