Differences between Playground and Project - xcode

Question

In the course of answering another question, I came across a weird bug in Playground. I have the following code to test if an object is an Array, Dictionary or a Set:
import Foundation
func isCollectionType(value : AnyObject) -> Bool {
let object = value as! NSObject
return object.isKindOfClass(NSArray)
|| object.isKindOfClass(NSDictionary)
|| object.isKindOfClass(NSSet)
}
var arrayOfInt = [1, 2, 3]
var dictionary = ["name": "john", "age": "30"]
var anInt = 42
var aString = "Hello world"
println(isCollectionType(arrayOfInt)) // true
println(isCollectionType(dictionary)) // true
println(isCollectionType(anInt)) // false
println(isCollectionType(aString)) // false
The code worked as expected when I put it into a Swift project or running it from the command line. However Playground wouldn't compile and give me the following error on the downcast to NSObject:
Playground execution failed: Execution was interrupted, reason: EXC_BAD_ACCESS (code=2, address=0x7fb1d0f77fe8).
* thread #1: tid = 0x298023, 0x00007fb1d0f77fe8, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=2, address=0x7fb1d0f77fe8)
* frame #0: 0x00007fb1d0f77fe8
frame #1: 0x000000010ba46e12 libswiftCore.dylib`Swift._EmptyArrayStorage._withVerbatimBridgedUnsafeBuffer (Swift._EmptyArrayStorage)<A>((Swift.UnsafeBufferPointer<Swift.AnyObject>) -> A) -> Swift.Optional<A> + 50
The build platform was OS X in all three cases. Does anyone know how to get Playground to play along?
Xcode 6.3.2. Swift 1.2. OS X 10.10.3 Yosemite

Answer 1

Not really the cause of that bug (it does look weird) but...
You will need to use optional chaining since value can be AnyObject:
import Foundation
func isCollectionType(value : AnyObject) -> Bool {
if let object = value as? NSObject {
return object.isKindOfClass(NSArray)
|| object.isKindOfClass(NSDictionary)
|| object.isKindOfClass(NSSet)
}
return false
}
var arrayOfInt = [1, 2, 3]
var dictionary = ["name": "john", "age": "30"]
var anInt = 42
var aString = "Hello world"
isCollectionType(arrayOfInt)
isCollectionType(dictionary)
isCollectionType(anInt)
isCollectionType(aString)
Also worth noting, NSArray and Array are different things:
NSArray is an immutable class:
#interface NSArray : NSObject <NSCopying, NSMutableCopying, NSSecureCoding, NSFastEnumeration>
whilst Array is a struct:
struct Array<T> : MutableCollectionType, Sliceable, _DestructorSafeContainer
With this in mind it might be surprising that isCollectionType(arrayOfInt) returns true - but there is a conversion happening.