Question

Assume following code,

NSString *str=[[NSString alloc] initWithString:@"sagar"];


[str autorelease];

I have seen many times that, Most of the programmers do prefer to put alloc, init simultaneously within one statement.

Here, I am asking for the possibility of dividing autorelease for next statement.

• For example, It is recommended to put init with alloc statement.
  Is it same for autorelease ?

Answer 1

Most of the programmers do prefer to put alloc, init simultaneously within one statement.

That’s because the instance returned by the initialiser is not necessarily the one returned by +alloc. For example, this is wrong and will crash your program:

NSString *str = [NSString alloc];
[str initWithString:@"sagar"];

because in this case -initWithString: causes the deallocation of the previous instance, and str ends up pointing to a deallocated object. This can be fixed by:

NSString *str = [NSString alloc];
str = [str initWithString:@"sagar"];

so that str points to the different instance returned by -initWithString:. The form:

NSString *str = [[NSString alloc] initWithString:@"sagar"];

guarantees that str points to the correct instance.

---

That said, -autorelease is different. Unless it’s been overridden by an evil djinn, it always returns the receiver itself. This means that both:

NSString *str = [[NSString alloc] initWithString:@"sagar"];
str = [str autorelease];

and:

NSString *str = [[NSString alloc] initWithString:@"sagar"];
[str autorelease];

are correct and work in the same manner.

As for the distinction between:

NSString *str = [[[NSString alloc] initWithString:@"sagar"] autorelease];

and:

NSString *str = [[NSString alloc] initWithString:@"sagar"];
…
[str autorelease];

some people prefer to use -autorelease in tandem with allocation to avoid forgetting to autorelease the instance later. Others prefer to place it in the return statement (if any):

NSString *str = [[NSString alloc] initWithString:@"sagar"];
…
return [str autorelease];

to make (more) explicit that the method/function returns an autoreleased object.