Swift 3

IndexSet can be created directly from an array literal using init(arrayLiteral:), like so:

let indices: IndexSet = [1, 2, 3]

Original answer (Swift 2.2)

Similar to pbasdf’s answer, but uses forEach(_:)

let array = [1,2,3,4,5,7,8,10]

let indexSet = NSMutableIndexSet()
array.forEach(indexSet.add) //Swift 3
//Swift 2.2: array.forEach{indexSet.addIndex($0)}

print(indexSet)