Nested arrays using Any/AnyObject - arrays

Question

According to Apple's official book "The Swift Programming Language (Swift 2.1)":
AnyObject can represent an instance of any class type.
Any can represent an instance of any type at all, including function types.
Knowing that, I wanted to emulate Python-like nested list using an Any array.
let array = [1, 2, [3, 4], [5, 6, [7, 8]], 1]
Since Int and Array are value types, I supposed that array would be typed as [Any]
But this wasn't the case here :
func flatten(list:[Any]) -> [Any] {
var new = [Any]()
for element in list {
if let array = element as? [Any] {
// this code never runs
let flattened = flatten(array)
for x in flattened {
new.append(y)
}
}else{
new.append(element)
}
}
return new
}
Note: calling this function gave me EXC_BAD_INSTRUCTION error at first until I did this tweak :
let array : [Any] = [1, 2, [3, 4], [5, 6, [7, 8]], 1]
Output : [1, 2, [3, 4], [5, 6, [7, 8]], 1]
Expected : [1, 2, 3, 4, 5, 6, 7, 8, 1]
Unexplained Solution:
I replaced everywhere in this example Any by AnyObject
Numbers now are of type NSNumber
func flatten(list:[AnyObject]) -> [AnyObject] {
var new = [AnyObject]()
for element in list {
if let array = element as? [AnyObject] {
let flattened = flatten(array)
for x in flattened {
new.append(y)
}
}else{
new.append(element)
}
}
return new
}
Output : [1, 2, 3, 4, 5, 6, 7, 8, 1]
Expected : [1, 2, 3, 4, 5, 6, 7, 8, 1]
Question :
Why is it working with [AnyObject] / NSArray and not with [Any], despite the fact that integer literals are mainly of type Int not NSNumber and array literals are of type Array and not NSArray? Is something wrong with my example?

Answer 1

When you use Any, Swift will wrap your nested array elements into NSArray and not into Swift arrays (which can't hold all Objective-C types). So your test if let array = element as? [Any] { will not be true if you use Any because the resulting array isn't of type [Any] but NSArray.
So if you want a function that manages Any you can change your test for:
if let nestedArray = element as? NSArray {
You then have to define a new flattenArray() function with an NSArray prototype:
func flattenArray(array: NSArray) -> [Any] {
var flattenedArray: [Any] = []
for element in array {
// We have an array
if let nestedArray = element as? NSArray {
flattenedArray = flattenedArray + flattenArray(nestedArray)
} else {
// We have a single element
flattenedArray.append(element)
}
}
return flattenedArray
}
func flattenArray(array: [Any]) -> [Any] {
var flattenedArray: [Any] = []
for element in array {
// We have an array
if let nestedArray = element as? NSArray {
flattenedArray = flattenedArray + flattenArray(nestedArray)
} else {
// We have a single element
flattenedArray.append(element)
}
}
return flattenedArray
}
and it will do the trick.
We could probably imagine a more elegant solution but with this example you get the idea behind this issue.