Why when I code I can do:
NSString *test;
test = @"stack";
test = @"overflow";
without any problems, NSString is not supposed to be immutable?
views:
82answers:
4
+6
A:
The string object is immutable. You are only changing the pointer to a different string.
Lou Franco
2010-08-06 22:27:59
+6
A:
It is immutable. You're not changing the underlying string with those statements, you're creating/using a brand new string. The pointer itself can change as often as you want but that's not the string.
paxdiablo
2010-08-06 22:28:22
And it's ok to do this or it's the wrong way to manipulate string.
alex
2010-08-06 22:33:56
It is the correct way to handle it. Whenever you do @"Some Text" you are really just creating an autoreleased instance of NSString.
peelman
2010-08-06 22:37:50
Ok, so when you use NSMutableString if you can do this with NSString, sorry if my question feels stupid.
alex
2010-08-06 22:48:38
@alex, there are no stupid questions, the pursuit of knowledge is rarely a bad thing. One reason you'd use a mutable string is if you didn't want to burden the garbage collector (GC takes time and fragmented memory can be a performance issue). Example: say you have a string that's always of the form 'User:14860' and the only thing that changes is the '14860' bit. You can use a mutable string and just change that bit (assuming length of '14860' is the same) which will not result in any objects becoming garbage-collectable. If instead you kept creating new strings, memory would soon fragment.
paxdiablo
2010-08-07 00:57:57
@paxdiablo - Actually, if he's working on the iPhone garbage collection really doesn't come into this. In his case, he'd need to worry about autoreleased strings piling up in an autorelease pool (particularly within a tight loop) or manually managing the memory for each. Also, object allocation / deallocation is one of the most expensive operations you can perform on the iPhone, and you can avoid that using a mutable string.
Brad Larson
2010-08-07 02:30:58
+1
A:
In your code you just "forget" about the old value (stack) and create a new string instance and fill it with "overflow"...
Michael Kessler
2010-08-06 22:28:53
+1
A:
Duplicate of the final word on nsstrings mutable and immutable ?
found though the first hit of Google(NSString immutable)
Peter M
2010-08-06 22:29:37