Why NSArray vs. NSMutableArray?

[Ajaxx]

Hi,
I am developing my first app and is using quite a few arrays to keep data.

I have been thinking about why (and when) to use NSArray over NSMutableArray?

Cheers

[TUX2K]

- NSArray: final, you cant add/remove item of this array.
- NSMutableArray: Mutable, you can add/remove item to this array, does take more memory than NSArray.

[fudgie_no1]

Originally Posted by Ajaxx

Hi,
I am developing my first app and is using quite a few arrays to keep data.

I have been thinking about why (and when) to use NSArray over NSMutableArray?

Cheers

Hi Ajaxx, I'm also in the process of creating my first app although coming towards the end now. When you grasp Arrays they are amazing! Someone may correct me but from what I understand...

NSArrays are immutable (the data inside them can't be changed)
NSMutableArrays are mutable (the data inside them can be changed)

So, if you just want to hold data and refer to it - use NSArrays.
If you want the data to be changable (i.e. using the replaceObjectAtIndex or addObject methods - Use NSMutableArrays.

hope that helps, if not the search facility will find you a dozen other answers to this I imagine, good luck!

[baja_yu]

That's correct. Same can be said of NSString and NSMutableString. But there are also copy and mutableCopy methods for creating both kinds of copies. Just one note about that:

- making a copy of a mutable string/array will create an immutable string/array

Other copying works as you might expect.

[RLScott]

I don't think anyone has really answered the OP's question. It is something I have wondered about too. What is the cost of using ..Mutable.. over the non-mutable version? In other words, why not use the ..Mutable.. versions all the time? I know there is more overhead in a mutable object - and probably more memory associated with it. But if the object has a short lifetime, and if there are not too many of them, it is unlikely that the added overhead would impact overall app performance. So, would anyone like to tackle that question?

[baja_yu]

That's a good question.

Being that it's a mobile platform, efficiency and optimization are of utmost importance. It's easy to get get sloppy in the desktop world with GBs or RAM and quad core CPUs working at 3+ GHz. But on a battery operated device with limited resources I think every bit helps.

Because of the huge resources I think many younger programmers aren't even aware of the terms optimization and efficiency. I've been at many schools/colleges and in most of them those topics aren't covered at all. Long gone are the days of Atari and Commodore 64, where all you had was 64KB or memory and a less than 1MHz CPU and you had to make the best of it. Programmers today are very spoiled.