This gist includes a quick syntax for constructing NSIndexSets—[@0:9] and [@0:9 step:2]—and fast enumeration support for NSIndexSet (yielding NSNumbers). The result is that you can enumerate over ranges using for/in. The gist is CodeRunner ready.

IndexSetEnumeration.m

#import <Foundation/Foundation.h>

@interface NSNumber (range)

- (NSIndexSet*):(NSUInteger)max;
- (NSIndexSet*):(NSUInteger)max step:(NSUInteger)step;

@end


@interface NSIndexSet (FastEnumeration) <NSFastEnumeration> @end

int main(int argc, char *argv[]) {
	@autoreleasepool {
		NSLog(@"vars = %@", [@0:20 step:2]);
		for(NSNumber * i in [@0:20 step:2]) {
			NSLog(@"i = %ld", i.integerValue);
		}
	}
}

@implementation NSNumber (range)

- (NSIndexSet*):(NSUInteger)max {
	return [self:max step:1];
}

- (NSIndexSet*):(NSUInteger)max step:(NSUInteger)step {
	NSMutableIndexSet * indexes = [NSMutableIndexSet new];
	for(NSUInteger i = self.unsignedIntegerValue; i <= max; i += step) {
		[indexes addIndex:i];
	}
	return indexes;
}

@end


@implementation NSIndexSet (FastEnumeration)

- (NSUInteger)countByEnumeratingWithState:(NSFastEnumerationState *)state objects:(__unsafe_unretained id *)stackbuf count:(NSUInteger)len {
	if(state->state == 0) {
		// There's no good way to check for mutations without access to NSMutableIndexSet's internals, so we just set a pointer that we know will be valid and won't change.
		state->mutationsPtr = state->extra;
	}
	
	NSUInteger index = [self indexGreaterThanOrEqualToIndex:state->state];
	if(index == NSNotFound) {
		return 0;
	}
	
	__autoreleasing NSNumber * temp = @(index);
	
	state->state = index + 1;
	state->itemsPtr = stackbuf;
	
	state->itemsPtr[0] = temp;
	
	return 1;
}

@end