How to access an array calling a category method within the method itself?

Question

I am new to Objective-C. I'm trying to create a category method for arrays that doesn't use a parameter. I'm told there is a way that the method can use this array without using the array as an argument. I haven't seen much specific to this question. Can anyone tell me how to access the array calling the method from within the category method?

I know using an argument works. Like this:

[array reversed:array];

I'm trying to do this instead:

[array reversed];

Answer 1

In your example, array is not calling anything. It is the object that the reversed message is passed to. Within the -reversed method, the object being passed the method (array in this case) is called self, which is how you would access it in a category, or any method of an object.

In your example, that would look something like:

@interface NSArray (Reversed)
- (NSArray *)reversed;
@end

@implementation NSArray (Reversed)

- (NSArray *)reversed {
    NSMutableArray *result = [NSMutableArray new];

    // Here is where you refer to the target as `self`
    for (id element in [self reverseObjectEnumerator]) {
        [result addObject: element];
    }
    return result;
}

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSArray *xs = @[@1, @2, @3];
        NSArray *reversed = [xs reversed];
        NSLog(@"%@ -> %@", xs, reversed);
    }
    return 0;
}