Swift check if NSNumber is Double

Question

So I'm trying to check whether NSNumber is Double or Int and I'm wondering if it's even possible.

I was hoping this will work, but it always returns true no matter with which type I'm comparing

var myDouble: Double = 0.0
var myNSNumber: NSNumber = NSNumber(value: myDouble)

if myNSNumber is Double {
    print("NSNumber is Double")
}else {
    print("NSNumber is different type")
}

In kotlin I'm using such Extension for Number which is NSNumber in swift and I want to recreate it in swift

protected operator fun Number.plus(other: Number): Number {
    return when (this) {
        is Long -> this.toLong() + other.toLong()
        is Int -> this.toInt() + other.toInt()
        is Short -> this.toShort() + other.toShort()
        is Byte -> this.toByte() + other.toByte()
        is Double -> this.toDouble() + other.toDouble()
        is Float -> this.toFloat() + other.toFloat()
    }
}

What do *you* mean by "is Double"? Do you actually want to check wether the value inside is properly representable as a `Double` or do you want to check wether the value that was used to create the `NSNumber` was originally a `Double`? — luk2302, May 24 '19 at 12:07
I want to check wether the value that was used to create the NSNumber was originally a Double — LeTadas, May 24 '19 at 12:08
May I ask: why? That must not matter to you unless you are doing some very weird things. — luk2302, May 24 '19 at 12:09
What @luk2302 said. Why not just call `myNSNumber.doubleValue` if you need a Double from an NSNumber? — Mark Thormann, May 24 '19 at 12:09
Maybe it's better you explained what you are trying to achieve with this, there might be a different way to do it rather than using NSNumber. I am also curious, in your kotlin code 3 + 3.5 = 6, is this intended behavior? — Joakim Danielson, May 24 '19 at 12:49

score 1 · Accepted Answer · answered May 24 '19 at 12:45

You can get type of the number stored using low-level CoreFoundation API:

extension NSNumber {
    var type: CFNumberType {
        return CFNumberGetType(self as CFNumber)
    }
}

And then you can use it.

Your plus function gonna be something like that:

extension NSNumber {
    func plus(other: NSNumber) -> NSNumber {
        switch type {
        case .sInt8Type, .charType:
            return NSNumber(value: self.int8Value + other.int8Value)
        case .sInt16Type, .shortType:
            return NSNumber(value: self.int16Value + other.int16Value)
        case .sInt32Type, .longType:
            return NSNumber(value: self.int32Value + other.int32Value)
        case .sInt64Type, .longLongType:
            return NSNumber(value: self.int64Value + other.int64Value)
        case .float32Type, .floatType:
            return NSNumber(value: self.floatValue + other.floatValue)
        case .float64Type, .doubleType:
            return NSNumber(value: self.doubleValue + other.doubleValue)
        case .intType, .cfIndexType, .nsIntegerType:
            return NSNumber(value: self.intValue + other.intValue)
        case .cgFloatType:
            switch MemoryLayout<CGFloat>.size {
            case 4:
                return NSNumber(value: self.floatValue + other.floatValue)
            default:
                return NSNumber(value: self.doubleValue + other.doubleValue)
            }
        }
    }
}

score -1 · Answer 2 · answered May 24 '19 at 12:51

-1

Try this code.

var myDouble: Double = 0.0
var myNSNumber: NSNumber = NSNumber(value: myDouble)

if myNSNumber.isKindOfClass(Double) {
    print("NSNumber is Double")
} else {
    print("NSNumber is different type")
}

answered May 24 '19 at 12:51

Wide Angle Technology

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Swift check if NSNumber is Double

2 Answers2