Determine that `true` is a Bool and not a number equal to 1

Question

Title is sub-optimal, suggestions welcome

Ran into a little trouble with Bool and numeric values. I want to determine if an AnyObject (from a JSON) is a Bool or a number.

So I need a test that will only succeed if the inserted type was truly a Bool or a number. Now it automatically converts and all statements are true.

let some : AnyObject = 1

if some is Bool {
    print("is Bool", some as! Bool)
}

if some is Int {
    print("is Int", some as! Int)
}

let some2 : AnyObject = false

if some2 is Bool {
    print("is Bool", some2 as! Bool)
}

if some2 is Int {
    print("is Int", some2 as! Int)
}

let some3 : AnyObject = 1.1

if some3 is Bool {
    print("is Bool", some3 as! Bool)
}

if some3 is Int {
    print("is Int", some3 as! Int)
}

What's the context of this? Doesn't whatever JSON lib your using already do this conversion? — Alexander, Jun 02 '16 at 16:46
@AMomchilov not using any JSON libs, I am working on a code generator that writes a Model based on a JSON. Type inference is done based on the value for a specific key. — R Menke, Jun 02 '16 at 16:49
Well the next obvious question is: why aren't you using a JSON lib? — Alexander, Jun 02 '16 at 16:51
@AMomchilov because much can be learned from trying things like this. My question is clearly not: "I have trouble with JSON", It is: "How do I circumvent this behaviour in Swift?" — R Menke, Jun 02 '16 at 16:52
@MartinR you are right, same question, but vadian's answer is really helpful — R Menke, Jun 02 '16 at 17:10

score 1 · Accepted Answer · answered Jun 02 '16 at 16:59

1

1, 1.0, true, all types are bridged to NSNumber

You can check the objCType

let some : AnyObject = true

if let type = String.fromCString(some.objCType) {
  switch type {
  case "c" : print("is Bool", some as! Bool)
  case "q" : print("is Int", some as! Int)
  case "d" : print("is Double", some as! Double)
  default :  print("no idea")
  }
} else {
  print("no matching objCType")
}

Source: Type Encodings

answered Jun 02 '16 at 16:59

vadian

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Perfect, I feared there was no way to do this. – R Menke Jun 02 '16 at 17:02
Just because you **can** doesn't mean you **should**. You'd be better off reworking this to use Generics, or at least `Any`. (Unlike `AnyObject`, primitives can be used with `Any` without bridging to NSNumber) – Alexander Jun 02 '16 at 17:03
@AMomchilov well I don't believe my experiments with JSON -> Swift Model with have far reaching real world effects..... – R Menke Jun 02 '16 at 17:04
4

This will detect `NSNumber(char: 65)` as a boolean ... – Martin R Jun 02 '16 at 17:04
I'm not saying they will, but this is just bad stuff to base your learning off anyway. You're bridging from Swift to Objective C, bridging to C to get a C string, then converting it back into a Swift String just to switch on it to do forced casting. This is gross. – Alexander Jun 02 '16 at 17:06
2

I haven't done much testing, but this *seems* to work better: http://stackoverflow.com/a/30223989/1187415. – Martin R Jun 02 '16 at 17:06
2

@MartinR Yes, of course, but I guess the purpose of the question is to get the numeric type out of JSON – vadian Jun 02 '16 at 17:06
@vadian that is true, the code above a just a mock – R Menke Jun 02 '16 at 17:07
1

@MartinR Yes, much better, but even still, this problem should be addressed at the root cause. This wouldn't be necessary if the source of the `AnyObject` was designed properly. – Alexander Jun 02 '16 at 17:10
2

@AMomchilov show me a way to receive data from a remote source as native Swift types and I will take it! – R Menke Jun 02 '16 at 17:12
1

On 32-bit platforms, `Int` would be encoded as "i", not "q". – Martin R Jun 02 '16 at 17:30
@MartinR All my tests just passed, thank you! – R Menke Jun 02 '16 at 17:35

Determine that `true` is a Bool and not a number equal to 1

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