Can I reuse my pointer after it's been added to a mutable array?

Let's say I've got an array with strings.

NSArray *names = [NSArray arrayWithObjects: @"One", @"Two", @"Three", nil];

What I want is to initiate objects of some custom class and them add them to a mutable array. I'm using a custom init method that takes a string argument.

To be more specific, I want to [SomeClass alloc] initWithName: aName] and add the resulting object to a NSMutableArray.

I'm thinking of using Objective-C fast enumeration. So what I get is:

NSMutableArray *objects = [NSMutableArray arrayWithCapacity: [names count];

for (NSString *name in names) {
    [objects addObject: [[[SomeClass alloc] initWithName: name] autorelease]];
}

The problem is that I can't add nil to the array and I don't like exception handling. However, my initiation method may return nil. So I decide to check first before adding (prevention). My new for-in-loop is:

SomeClass *someObject;

for (NSString *name in names) {
    someObject = [[[SomeClass alloc] initWithName: name] autorelease];
    if (someObject) {
        [o开发者_运维问答bjects addObject: someObject];
    }
}

Now, instead of immediately passing the new object to the array, I'm setting up a pointer someObject first and then passing the pointer to the array instead.

This example raises a question to me. When I someObject = [[[SomeClass alloc] initWithName: name] autorelease] in the loop, do the existing objects (which are added using the same pointer) in the array change too?

To put it in other words: does the addObject: (id)someObject method make a new internal copy of the pointer I pass or do I have to create a copy of the pointer — I don't know how — and pass the copy myself?

Thanks a lot! :-)

It's fine to reuse someObject; if you think about it, you're already reusing name each time you go through the loop.

-addObject: may or may not copy the object that you pass in. (It doesn't -- it retains the object rather than copying it, but it's conceivable that some NSMutableArray subclass could copy instead.) The important thing is that this code really shouldn't care about what -addObject: does.

Also, don't lose sight of the distinction between a pointer and the object that it points to. Pointers are just references, and a pointer is copied each time you pass it into a method or function. (Like C, Objective-C passes parameters by value, so passing a pointer into a method results in putting the value of the pointer on the stack.) The object itself isn't copied, however.

Short answer: no, you don't have to worry about reusing someObject.

Slightly longer answer: the assignment—someObject = ... assigns a new pointer value to the someObject variable; addObject: is then getting that value, not the address of someObject itself.

I think you're getting confused in the concept of pointer here. When you say someObject = [[[SomeClass alloc] init... you are basically pointing the someObject pointer to a new object. So to answer your question- your current code is fine.

As for whether arrays maintain copies of the objects added to them - NO, the array retains the object you add to it. However, that doesn't matter to your code above.

Three20 provides the answer!