Question

I’ve got an array of NSNumber objects created thusly:

        myArray = [[NSMutableArray alloc] initWithObjects:[NSNumber numberWithDouble:0.0],
                [NSNumber numberWithDouble:0.0],
                [NSNumber numberWithDouble:0.0],
                [NSNumber numberWithDouble:0.0],
                [NSNumber numberWithDouble:0.0], nil];

(Though just occurred to me that I could have done

myArray = [NSMutableArray arrayWithObjects: object1, etc..., nil];

and skipped the alloc entirely. Which would be better?)

Anyway, it’s tangential to my question:

Over the life of the app, the values get changed. At a certain point, I want to reset them all to zero. Here’s how I’m doing it now:

 for (NSNumber *number in myArray) {
     number = [NSNumber numberWithDouble:0.0];
 }

But the Static Analyzer throws a warning because it thinks ‘number’ is an unused variable (which it technically is – set and then never used again). Is there a better way to zero out all the elements of the array? Perhaps replace the array with a new one? What would be fastest and avoid the static analysis warning?

Answer 1

With regards to creating an array, remember that alloc+initWithObjects: requires an explicit release afterwards, whereas the arrayWithObjects: convenience method does not (and also, it will not survive an iteration of the run loop unless you retain it).

for (NSNumber *number in myArray) {
    number = [NSNumber numberWithDouble:0.0];
}

This loop doesn’t do what you think it does. number simply points to an NSNumber instance, and all you’re doing is changing number to point to another instance of NSNumber, it does not modify the original instance of NSNumber in myArray.

NSNumber instances are immutable, so the only way to set them all to zero would be to completely erase the contents of myArray and fill it back up with [NSNumber numberWithDouble:0.0]

NSUInteger count = [myArray count];
[myArray removeAllObjects];

while(count--)
    [myArray addObject:[NSNumber numberWithDouble:0.0]];