So I'm messing around with iTunesLibrary and I am loading test data into a structure. One of the structure properties is an array of track persistentID's. So, I setup the array as such:

var tracks:Array<NSNumber> = [8531377916780748525,10894448951054098798,1913808070485867300,3944816338394235389,930561036379062783,3251308436698647533,14952971713326701209,14970963935055520988,14311328294714471790,8057477945548486586]

Playground does the same thing.

These numbers came from the iTunesLibrary persistentID's for specific tracks, so why don't they work? All I'm doing is manually adding a few track persistentID's to an array for testing purposes. How can an NSNumber not fit within an NSNumber?

I'm not 100% certain this is the answer, but see my post in your previous thread... Dictionary and NSNumber overflow errors

And here's what I did to make your code work:

var tracks:Array<NSNumber> = [
    8531377916780748525,
    10894448951054098798,
    1913808070485867300,
    3944816338394235389,
    930561036379062783,
    3251308436698647533,
    14952971713326701209,
    14970963935055520988,
    14311328294714471790,
    8057477945548486586
    ].map { $0 as UInt64 as NSNumber }

Yeah, I has seen a post where they recommended using UInt64 because there are issues with NSNumber. I guess I'll just refactor what I've written. It's not like I'll be writing to the iTunesLibrary.

Oh wait. I now see what you did there. I'll give that a try before refactoring!