Obj-C: [NSString stringWithString:@"string"] vs. @"string"

Question

I've seen people do something like [NSString stringWithString:@"some string"]. Why not just do @"some string"?

For an example, look at the facebook-ios-sdk.

+[NSString stringWithString:] -- what's the point? is a similar question, but none of the answers address [NSString stringWithString:@"some string"] vs. @"some string".

[NSString stringWithString:@"some string"] copies @"some string" from read-only memory, which is baked in the executable, but as NSString is immutable anyways, I don't see the point either. — user142019
– user142019, Commented Jun 8, 2011 at 15:02
Now we have to use @"some string", otherwise we get this warning "Using 'stringWithString': with a literal is redundant" — Jun
– Jun, Commented Jul 17, 2013 at 10:42

anon · Accepted Answer · 2011-06-08 15:09:03Z

9

Actually there is no difference. [NSString stringWithString: str] just does nothing and returns str if str is immutable already.

answered Jun 8, 2011 at 15:09

anon

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JeremyP · Accepted Answer · 2011-06-08 15:12:00Z

7

There's no difference other than the extra key strokes needed. In fact, with a constant string as a parameter (or an immutable string) you just get another pointer to the parameter.

The main use of the method is in subclasses:

[NSMutableString stringWithString: @"fdghdfjl"];

will give you a mutable autoreleased copy of the original.

answered Jun 8, 2011 at 15:12

JeremyP

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1 Comment

Chuck Over a year ago

It's also used as an alternative to [[someString copy] autorelease] — that is, it guarantees that you have an non-owned immutable string — that some people find more readable, I think.

drekka · Accepted Answer · 2011-11-04 00:48:41Z

3

One thing to note about stringWithString: is that it will throw an exception if the source string is nil.

answered Nov 4, 2011 at 0:48

drekka

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