Fast enumeration on an NSIndexSet

Question

Can you fast enumerate a NSIndexSet? if not, what's the best way to enumerate the items in the set?

Ornamented

Answer 1

Fast enumeration must yield objects; since an NSIndexSet contains scalar numbers (NSUIntegers), not objects, no, you cannot fast-enumerate an index set.

Hypothetically, it could box them up into NSNumbers, but then it wouldn't be very fast.

Balikpapan

I don't mind the performance hit, but you'd have to slow enumerate before you fast enumerate, right? – Bringingup

With tagged pointers (on 64-bit platforms since OS X 10.7 and iOS 5), NSIndexSet fast enumeration ought to be pretty fast. – Batfish

Answer 2

In OS X 10.6+ and iOS SDK 4.0+, you can use the -enumerateIndexesUsingBlock: message:

NSIndexSet *idxSet = ...

[idxSet enumerateIndexesUsingBlock:^(NSUInteger idx, BOOL *stop) {
  //... do something with idx
  // *stop = YES; to stop iteration early
}];

Apriorism

Change NSInteger to NSUInteger – Duff

This is the actual answer, can asker change? – Nenitanenney

Worth noting that this is also available in iOS SDK 4.0+ – Ponderable

Answer 3

A while loop should do the trick. It increments the index after you use the previous index.

/*int (as commented, unreliable across different platforms)*/
NSUInteger currentIndex = [someIndexSet firstIndex];
while (currentIndex != NSNotFound)
{
    //use the currentIndex

    //increment
    currentIndex = [someIndexSet indexGreaterThanIndex: currentIndex];
}

Czar

Valid indexes can exceed the range of values representable by int, since indexes are unsigned. Further, when targeting a 64-bit platform or building with NS_BUILD_32_LIKE_64 defined, the index is a 64-bit value. Use NSUInteger instead of int in order to match the type stored by NSIndexSet under all platforms. – Schaub

@Jeremy W. Sherman: actually the indexes are effectively limited to those values that can be represented by a positive NSInteger because the "not found" return value is NSNotFound which is the same as NSIntegerMax – Bessiebessy

@Evan: this example is still wrong. The comparison in the while loop needs to be against NSNotFound not -1. – Bessiebessy

@Evan: Interesting. I was using the Apple developer documentation as a reference. It seems a little experimentation is needed... developer.apple.com/library/mac/#DOCUMENTATION/Cocoa/Reference/… – Bessiebessy

@Evan Mulawski: Just verified that the Apple documentation is correct. -indexGreaterThanIndex: does return NSNotFound, not -1. The issue in the discussion occurs because he like you was using the wrong return type. – Bessiebessy

@Bessiebessy Wow, I never before noticed that using a signed NSNotFound halves the range of index values NSUInteger could represent if NSNotFound were instead NSUIntegerMax. I suppose NSNotFound is NSIntegerMax so as to agree with kCFNotFound; the CFIndex type used by CF collections is a signed long. @EveryoneElse Even with indices capped at NSNotFound (NSIntegerMax), int is still the wrong choice to store an index, because the range of NSInteger exceeds the range of int in 64-bit builds and builds with NS_BUILD_32_LIKE_64 defined. – Schaub

Answer 4

Short answer: no. NSIndexSet does not conform to the <NSFastEnumeration> protocol.

Glamorize

what about enumerateIndexesUsingBlock:^(NSUInteger idx, BOOL *stop) {} --- is this not fast enumeration? – Bassist

Answer 5

Supposing you have an NSTableView instance (let's call it *tableView), you can delete multiple selected rows from the datasource (uhm.. *myMutableArrayDataSource), using:

[myMutableArrayDataSource removeObjectsAtIndexes:[tableView selectedRowIndexes]];

[tableView selectedRowIndexes] returns an NSIndexSet. No need to start enumerating over the indexes in the NSIndexSet yourself.

Boff

This isn't actually answering the question, but rather saying "maybe you didn't need to ask that question to start with. What do you want this fast enumeration for?" – Bassist

Answer 6

These answers are no longer true for IndexSet in Swift 5. You can perfectly get something like:

let selectedRows:IndexSet = table.selectedRowIndexes

and then enumerate the indices like this:

for index in selectedRows {
   // your code here.
}

Beltane