Looping using NSRange

Question

I'm trying to use NSRange to hold a range of years, such as

NSRange years = NSMakeRange(2011, 5);

I know NSRange is used mostly for filtering, however I want to loop over the elements in the range. Is that possible without converting the NSRange into a NSArray?

Answer 1

It kind of sounds like you're expecting NSRange to be like a Python range object. It's not; NSRange is simply a struct

typedef struct _NSRange {
       NSUInteger location;
       NSUInteger length;
} NSRange;

not an object. Once you've created one, you can use its members in a plain old for loop:

NSUInteger year;
for(year = years.location; year < NSMaxRange(years); year++ ){
    // Do your thing.
}

(Still working on the assumption that you're thinking about Python.) There's syntax in ObjC called fast enumeration for iterating over the contents of an NSArray that is pleasantly similar to a Python for loop, but since literal and primitive numbers can't be put into an NSArray, you can't go directly from an NSRange to a Cocoa array.

A category could make that easier, though:

@implementation NSArray (WSSRangeArray)

+ (id)WSSArrayWithNumbersInRange:(NSRange)range
{
    NSMutableArray * arr = [NSMutableArray array];
    NSUInteger i;
    for( i = range.location; i < NSMaxRange(range); i++ ){
        [arr addObject:[NSNumber numberWithUnsignedInteger:i]];
    }

    return arr;
}

Then you can create an array and use fast enumeration:

NSArray * years = [NSArray WSSArrayWithNumbersInRange:NSMakeRange(2011, 5)];
for( NSNumber * yearNum in years ){
    NSUInteger year = [yearNum unsignedIntegerValue];
    // and so on...
}