NSIndexSet “-indexAtIndex:”?

Question

This feels like a dumb question because it seems to me like my use case must be quite common.

Say I want to represent a sparse set of indexes with an NSIndexSet (whi

Answer 1

NSIndexSet isn't designed for that sort of access. Usually, you enumerate through the indexes in a set like so:

NSUInteger idx = [theSet indexGreaterThanOrEqualToIndex: 0];
while (idx != NSNotFound) {
    // idx equals the next index in the set.
    idx = [theSet indexGreaterThanIndex: idx];
}

@Richard points out this for loop is simpler:

for (NSUInteger i = [indexSet firstIndex]; i != NSNotFound; i = [indexSet indexGreaterThanIndex:i]) {
    // i equals the next index in the set.
}

There's some block-based methods that are new to NSIndexSet as of Mac OS X 10.6/iOS 4.0, but I haven't reviewed them as of yet.

It should be trivial to modify the above example to keep a running count of indexes and stop when it reaches the fourth index in the set. ;)