How do I make and use a Queue in Objective-C?

Question

I want to use a queue data structure in my Objective-C program. In C++ I\'d use the STL queue. What is the equivalent data structure in Objective-C? How do I push/pop ite

Answer 1

As far as I know, Objective-C does not provide a Queue data structure. Your best bet is to create an NSMutableArray, and then use [array lastObject], [array removeLastObject] to fetch the item, and [array insertObject:o atIndex:0]...

If you're doing this a lot, you might want to create an Objective-C category to extend the functionality of the NSMutableArray class. Categories allow you to dynamically add functions to existing classes (even the ones you don't have the source for) - you could make a queue one like this:

(NOTE: This code is actually for a stack, not a queue. See comments below)

@interface NSMutableArray (QueueAdditions)

- (id)pop;
- (void)push:(id)obj;

@end

@implementation NSMutableArray (QueueAdditions)

- (id)pop
{
    // nil if [self count] == 0
    id lastObject = [[[self lastObject] retain] autorelease];
    if (lastObject)
        [self removeLastObject];
    return lastObject;
}

- (void)push:(id)obj
{
     [self addObject: obj];
}

@end