Sort Array Question

I am wondering what is happening behind the scenes here. The code works fine but I was kind of expecting it to add the sorted object to the Array.

I created a Class called BoilerPlateCode which I am putting often used methods in to that I will need to call. I wrote a method that sorts an NSArray and returns NSMutableArray.

Code:

-(NSMutableArray*)sortArray: (NSArray*) incomingArray{
    NSArray *tempArray = [incomingArray sortedArrayUsingSelector:@selector(localizedCaseInsensitiveCompare:)];
    NSMutableArray * makeMutableArray = [NSArray arrayWithArray:tempArray];
    
    return makeMutableArray;
}

I then call it like this

Code:

    BoilerPlateCode *bpc = [[BoilerPlateCode alloc] init];
    staticSkills = [[NSMutableArray alloc] initWithObjects:@"Demon Lore", @"Sword",@"Preception",@"Surgery", @"Tracking",nil];
    staticSkills = [bpc sortArray: staticSkills];

My question is... The last line of code "staticSkills = [bpc sortArray: staticSkills];" takes the Array, sorts it and then returns it to the same Array object. Since I never removed the objects from the array in the first place I would think that it would have an accumulative result with a duplicate set of objects in it since it is a mutableArray?

 

I have never used class method before in my own classes. I have always instantiated an object to use them. Perhaps this is a good chance to start using them and get comfortable with them.

Thanks for the explanation of the array. I see what is happening.

 

This whole method seemed like it suffered from an extra step when I wrote it. I first wrote the line of code that sorts the array as a mutable array but I got an error about the return type being an NSArray.

Since the user will add objects to this array I had to keep it mutable so I had to take the extra step of creating a new mutable Array and assigning the non mutable array to it before returning it.

But your response brought up another question as I am still working on figuring out the behind the scenes with pointers and such. I always have to remind myself that I am working with pointers.

So this code.

Code:

NSMutableArray * makeMutableArray = [NSArray arrayWithArray:tempArray];

So with this code I am saying that I am using the "arrayWithArray" Method from the NSArray Class that is taking a pointer argument to an NSArray called tempArray. I then create a new object of type NSMutableArray which I assign the pointer makeMutableArray to that memory location.

So basically now I am assigning the tempArray pointer to the makeMutableArray pointer and the makeMutableArray pointer is simply pointing to the tempArray memory location?

Is this why you say it is not doing what I thought it was?

Thanks again for your help.

 

Gotcha, Thanks Duncan.

 

So an NSArray can not be sorted in place because it is not mutable, it is what it is. So sorting an NSArray creates a new array object.

If you try an reassign the same pointer to the array it will have the same name but pointed to a different memory address, correct?

So myNSArray = [myNSArray sortArray......]; will this create a new pointer with the same name to a different memory address for the newly created array?

And myNSMutableArray = [myNSMutbaleArray sortArray.....]; This will just rearrange the mutablearray and not create a new pointer?

Thanks again. I am trying to learn more about the internal working. It is so easy sometime to find some code online that works and you just except it and don't question why it works. I'm constantly having to remind myself that I work with pointers to objects instead of objects themselves.

But I really enjoy programming and learning.

 

Got that now, thank you.

NSArrays as "set-in-stone" arrays once created. They can't sort themselves but return a new array object that has been sorted.

Do NSArrays take up less memory because they are defined and can't be changed?