Inconsistencies with NSNull and `===`

[bbrk24]

  1> import Foundation
  2> let x: NSNull? = nil
x: Foundation.NSNull? = nil
  3> x === x
$R0: Bool = false
  4> x !== x
$R1: Bool = false
  5> NSNull() === NSNull()
$R2: Bool = true
  6> NSNull() !== NSNull()
$R3: Bool = true

[parkera]

In Objective-C we can make sure that NSNull is a singleton when initialized with init(). In Swift we don't have a mechanism to do that, so we ended up with this hack:

public func ===(lhs: NSNull?, rhs: NSNull?) -> Bool {
    guard let _ = lhs, let _ = rhs else { return false }
    return true
}

It seems like that could be fixed.

[bbrk24]

Yeah, it should probably be something like (untested)

public func === (lhs: NSNull?, rhs: NSNull?) -> Bool {
  switch (lhs, rhs) {
    case (nil, nil):
      return true
    case (nil, _), (_, nil):
      return false
    default: 
      return true
  }
}

public func !== (lhs: NSNull?, rhs: NSNull?) -> Bool {
  return !(lhs === rhs)
}