Setting an object during fast enumeration problems

Question

A day or so ago I posted this question: Confused about enumeration... How do I change the objects that during enumeration?

I learned that I can call methods on an object during enumeration, but if I assign using the "=" operator then it creates a new object (not what I want).

The linked question shows how to use setString on an array of NSString objects... but now my question is for custom objects

Here's what I want to do

for (Car * car in self.carsArray)
{
    if (car.name == nil){
      car = [self getrandomCar];         
    }
}

However, the "=" operator isn't going to work for me... is there some type of method I can use like this?

[car setObject:[self getrandomCar];

Thanks!

hatkirby · Accepted Answer · 2011-10-08 02:15:23Z

8

First of all, if you want to change the object pointed to in the array, you have to change the array, not the pointer the fast enumeration gives you. Second, you can't change the array during fast enumeration (~~well, you can, but~~ it will blow up in your face). I suggest you make a copy of the array before enumeration and then modify that during enumeration, throwing out the original array after enumeration is done. For example:

tempArray = [self.carsArray mutableCopy];

for (Car * car in self.carsArray)
{
    if (car.name == nil){
      [tempArray replaceObjectAtIndex:[self.carsArray indexOfObject:car] withObject:[self getrandomCar]];
    }
}

[self.carsArray release];
self.carsArray = [tempArray copy];
[tempArray release];
tempArray = nil;

It's not as pretty as fast enumeration would have you believe, but it's what has to be done if you want to change the array while enumerating through it.

edited Oct 8, 2011 at 2:15

answered Oct 8, 2011 at 0:04

hatkirby

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1 Comment

jscs Over a year ago

There's no "you can, but" about it -- trying to mutate an array you're enumerating over throws an exception every time.

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