Question

Should I always release self when there is a failure inside init, or should I only do so if I have initialized instance variables first?

To put it another way, is this pattern valid? Is there a time when I shouldn’t release self inside an init method, or should I assume that if the control flow enters init, self has at least a retain count of 1?

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

 //do some init stuff
 if (somethingFailed)
 {
  [self release];
  return nil;
 }
 return self;
}

Answer 1

If some check you need in your initialization method fails, then yes you should release self. Note however, that if [super init] returns nil it does not make sense to send release to self as self is nil. This is actually frowned on by Apple:

You should only call [self release] at the point of failure. If you get nil back from an invocation of the superclass’s initializer, you should not also call release.

Example:

- (id)init
{
   self = [super init];
   if(self) {
       // do some init stuff

       if (somethingFailed)
       {
          [self release]
          self = nil;
       }
   }

   return self;
}

Also see the Mac Dev Center documentation on Handling Initialization Failure