Swift converting between UInt and Int

Question

I have the following methods

var photos = [MWPhoto] = [MWPhoto]()

func numberOfPhotosInPhotoBrowser(photoBrowser: MWPhotoBrowser!) -> UInt {

    return self.photos.count
}

func photoBrowser(photoBrowser: MWPhotoBrowser!, photoAtIndex index: UInt) -> MWPhotoProtocol! {

    return self.photos[index]
}

However for the first I get Int is not convertible to UInt (since self.photos.count is an Int

and for the second UInt is not convertible to Int - since the self.photos[ can only take an Int for its index.

How can I correctly convert the UInt to Int and back?

Answer 1

In the first one, the return type is UInt , but you return Int since count returns Int.

Basically UInt has initializer which take variants of value types arguments such as Int, CGFloat, Double or event string and return a new value type.

• UInt(8) // result is 8 UInt value type
• UInt(20.12) // result is 20 UInt value type
• UInt(Double(10)) // result is 10 UInt value type
• UInt("10") // result is 10 UInt value type, note this is failable initializer, can be a value or nil

-

func numberOfPhotosInPhotoBrowser(photoBrowser: MWPhotoBrowser!) -> UInt {

    return UInt(self.photos.count)
}

For the second one, the array subscript expects Int value where you are passing UInt , so create a new Int value type from UInt ,

func photoBrowser(photoBrowser: MWPhotoBrowser!, photoAtIndex index: UInt) -> MWPhotoProtocol! {

    return self.photos[Int(index)]
}

Answer 2

// initializing Int
var someInt: Int = 8
someInt

// Converting Int to UInt
var someIntToUInt: UInt = UInt(someInt)
someIntToUInt

// initializing UInt   
var someUInt: UInt = 10
someUInt

// Converting UInt to Int   
var someUIntToInt: Int = Int(someUInt)
someUIntToInt

Answer 3

If you want unsigned int from negative value use UInt(bitPattern:)

let intVal = -1
let uintVal = UInt(bitPattern: intVal) // uintVal == 0xffffffffffffffff

Answer 4

Add this anywhere outside of a class:

extension UInt {
    /// SwiftExtensionKit
    var toInt: Int { return Int(self) }
}

Then just call:

self.photos[index].toInt

Answer 5

I got so frustrated with Swift's cryptic method parameters bitPattern: and truncatingBitPattern: and my inability to remember which one to use when, that I created the following class containing a large number of conversion methods.

I'm not necessarily recommending that you include this in your program. I'm sure many people will say that Swift is trying to protect us from ourselves and that sabotaging that effort is dumb. So maybe you should just keep this file somewhere as a kind of cheat sheet so you can quickly determine how to do a conversion, and copy the parameters into your program when needed.

Incidentally, JDI stands for "just do it".

/// Class containing a large number of static methods to convert an Int to a UInt or vice-versa, and 
/// also to perform conversions between different bit sizes, for example UInt32 to UInt8.
///
/// Many of these "conversions" are trivial, and are only included for the sake of completeness.
///
/// A few of the conversions involving Int and UInt can give different results when run on 32-bit
/// and 64-bit systems. All of the conversion where the bit size of both the source and the target
/// are specified will always give the same result independent of platform.
public class JDI {

   // MARK: - To signed Int

   // To Int8
   public static func ToInt8(_ x : Int8) -> Int8 {
      return x
   }
   public static func ToInt8(_ x : Int32) -> Int8 {
      return Int8(truncatingBitPattern: x)
   }
   public static func ToInt8(_ x : Int64) -> Int8 {
      return Int8(truncatingBitPattern: x)
   }
   public static func ToInt8(_ x : Int) -> Int8 {
      return Int8(truncatingBitPattern: x)
   }
   public static func ToInt8(_ x : UInt8) -> Int8 {
      return Int8(bitPattern: x)
   }
   public static func ToInt8(_ x : UInt32) -> Int8 {
      return Int8(truncatingBitPattern: x)
   }
   public static func ToInt8(_ x : UInt64) -> Int8 {
      return Int8(truncatingBitPattern: x)
   }
   public static func ToInt8(_ x : UInt) -> Int8 {
      return Int8(truncatingBitPattern: x)
   }

   // To Int32
   public static func ToInt32(_ x : Int8) -> Int32 {
      return Int32(x)
   }
   public static func ToInt32(_ x : Int32) -> Int32 {
      return x
   }
   public static func ToInt32(_ x : Int64) -> Int32 {
      return Int32(truncatingBitPattern: x)
   }
   public static func ToInt32(_ x : Int) -> Int32 {
      return Int32(truncatingBitPattern: x)
   }
   public static func ToInt32(_ x : UInt8) -> Int32 {
      return Int32(x)
   }
   public static func ToInt32(_ x : UInt32) -> Int32 {
      return Int32(bitPattern: x)
   }
   public static func ToInt32(_ x : UInt64) -> Int32 {
      return Int32(truncatingBitPattern: x)
   }
   public static func ToInt32(_ x : UInt) -> Int32 {
      return Int32(truncatingBitPattern: x)
   }

   // To Int64
   public static func ToInt64(_ x : Int8) -> Int64 {
      return Int64(x)
   }
   public static func ToInt64(_ x : Int32) -> Int64 {
      return Int64(x)
   }
   public static func ToInt64(_ x : Int64) -> Int64 {
      return x
   }
   public static func ToInt64(_ x : Int) -> Int64 {
      return Int64(x)
   }
   public static func ToInt64(_ x : UInt8) -> Int64 {
      return Int64(x)
   }
   public static func ToInt64(_ x : UInt32) -> Int64 {
      return Int64(x)
   }
   public static func ToInt64(_ x : UInt64) -> Int64 {
      return Int64(bitPattern: x)
   }
   public static func ToInt64(_ x : UInt) -> Int64 {
      return Int64(bitPattern: UInt64(x))  // Does not extend high bit of 32-bit input
   }

   // To Int
   public static func ToInt(_ x : Int8) -> Int {
      return Int(x)
   }
   public static func ToInt(_ x : Int32) -> Int {
      return Int(x)
   }
   public static func ToInt(_ x : Int64) -> Int {
      return Int(truncatingBitPattern: x)
   }
   public static func ToInt(_ x : Int) -> Int {
      return x
   }
   public static func ToInt(_ x : UInt8) -> Int {
      return Int(x)
   }
   public static func ToInt(_ x : UInt32) -> Int {
      if MemoryLayout<Int>.size == MemoryLayout<Int32>.size {
         return Int(Int32(bitPattern: x))  // For 32-bit systems, non-authorized interpretation
      }
      return Int(x)
   }
   public static func ToInt(_ x : UInt64) -> Int {
      return Int(truncatingBitPattern: x)
   }
   public static func ToInt(_ x : UInt) -> Int {
      return Int(bitPattern: x)
   }

   // MARK: - To unsigned Int

   // To UInt8
   public static func ToUInt8(_ x : Int8) -> UInt8 {
      return UInt8(bitPattern: x)
   }
   public static func ToUInt8(_ x : Int32) -> UInt8 {
      return UInt8(truncatingBitPattern: x)
   }
   public static func ToUInt8(_ x : Int64) -> UInt8 {
      return UInt8(truncatingBitPattern: x)
   }
   public static func ToUInt8(_ x : Int) -> UInt8 {
      return UInt8(truncatingBitPattern: x)
   }
   public static func ToUInt8(_ x : UInt8) -> UInt8 {
      return x
   }
   public static func ToUInt8(_ x : UInt32) -> UInt8 {
      return UInt8(truncatingBitPattern: x)
   }
   public static func ToUInt8(_ x : UInt64) -> UInt8 {
      return UInt8(truncatingBitPattern: x)
   }
   public static func ToUInt8(_ x : UInt) -> UInt8 {
      return UInt8(truncatingBitPattern: x)
   }

   // To UInt32
   public static func ToUInt32(_ x : Int8) -> UInt32 {
      return UInt32(bitPattern: Int32(x))  // Extend sign bit, assume minus input significant
   }
   public static func ToUInt32(_ x : Int32) -> UInt32 {
      return UInt32(bitPattern: x)
   }
   public static func ToUInt32(_ x : Int64) -> UInt32 {
      return UInt32(truncatingBitPattern: x)
   }
   public static func ToUInt32(_ x : Int) -> UInt32 {
      return UInt32(truncatingBitPattern: x)
   }
   public static func ToUInt32(_ x : UInt8) -> UInt32 {
      return UInt32(x)
   }
   public static func ToUInt32(_ x : UInt32) -> UInt32 {
      return x
   }
   public static func ToUInt32(_ x : UInt64) -> UInt32 {
      return UInt32(truncatingBitPattern: x)
   }
   public static func ToUInt32(_ x : UInt) -> UInt32 {
      return UInt32(truncatingBitPattern: x)
   }

   // To UInt64
   public static func ToUInt64(_ x : Int8) -> UInt64 {
      return UInt64(bitPattern: Int64(x))  // Extend sign bit, assume minus input significant
   }
   public static func ToUInt64(_ x : Int32) -> UInt64 {
      return UInt64(bitPattern: Int64(x))  // Extend sign bit, assume minus input significant
   }
   public static func ToUInt64(_ x : Int64) -> UInt64 {
      return UInt64(bitPattern: x)
   }
   public static func ToUInt64(_ x : Int) -> UInt64 {
      return UInt64(bitPattern: Int64(x))  // Extend sign bit if necessary, assume minus input significant
   }
   public static func ToUInt64(_ x : UInt8) -> UInt64 {
      return UInt64(x)
   }
   public static func ToUInt64(_ x : UInt32) -> UInt64 {
      return UInt64(x)
   }
   public static func ToUInt64(_ x : UInt64) -> UInt64 {
      return x
   }
   public static func ToUInt64(_ x : UInt) -> UInt64 {
      return UInt64(x)  // Does not extend high bit of 32-bit input
   }

   // To UInt
   public static func ToUInt(_ x : Int8) -> UInt {
      return UInt(bitPattern: Int(x))  // Extend sign bit, assume minus input significant
   }
   public static func ToUInt(_ x : Int32) -> UInt {
      return UInt(truncatingBitPattern: Int64(x))  // Extend sign bit, assume minus input significant
   }
   public static func ToUInt(_ x : Int64) -> UInt {
      return UInt(truncatingBitPattern: x)
   }
   public static func ToUInt(_ x : Int) -> UInt {
      return UInt(bitPattern: x)
   }
   public static func ToUInt(_ x : UInt8) -> UInt {
      return UInt(x)
   }
   public static func ToUInt(_ x : UInt32) -> UInt {
      return UInt(x)
   }
   public static func ToUInt(_ x : UInt64) -> UInt {
      return UInt(truncatingBitPattern: x)
   }
   public static func ToUInt(_ x : UInt) -> UInt {
      return x
   }
}

Here's some test code:

   public func doTest() {

      // To Int8

      assert(JDI.ToInt8(42 as Int8) == 42)
      assert(JDI.ToInt8(-13 as Int8) == -13)

      assert(JDI.ToInt8(42 as Int32) == 42)
      assert(JDI.ToInt8(257 as Int32) == 1)

      assert(JDI.ToInt8(42 as Int64) == 42)
      assert(JDI.ToInt8(257 as Int64) == 1)

      assert(JDI.ToInt8(42 as Int) == 42)
      assert(JDI.ToInt8(257 as Int) == 1)

      assert(JDI.ToInt8(42 as UInt8) == 42)
      assert(JDI.ToInt8(0xf3 as UInt8) == -13)

      assert(JDI.ToInt8(42 as UInt32) == 42)
      assert(JDI.ToInt8(0xfffffff3 as UInt32) == -13)

      assert(JDI.ToInt8(42 as UInt64) == 42)
      assert(JDI.ToInt8(UInt64.max - 12) == -13)

      assert(JDI.ToInt8(42 as UInt) == 42)
      assert(JDI.ToInt8(UInt.max - 12) == -13)

      // To Int32

      assert(JDI.ToInt32(42 as Int8) == 42)
      assert(JDI.ToInt32(-13 as Int8) == -13)

      assert(JDI.ToInt32(42 as Int32) == 42)
      assert(JDI.ToInt32(-13 as Int32) == -13)

      assert(JDI.ToInt32(42 as Int64) == 42)
      assert(JDI.ToInt32(Int64(Int32.min) - 1) == Int32.max)

      assert(JDI.ToInt32(42 as Int) == 42)
      assert(JDI.ToInt32(-13 as Int) == -13)

      assert(JDI.ToInt32(42 as UInt8) == 42)
      assert(JDI.ToInt32(0xf3 as UInt8) == 243)

      assert(JDI.ToInt32(42 as UInt32) == 42)
      assert(JDI.ToInt32(0xfffffff3 as UInt32) == -13)

      assert(JDI.ToInt32(42 as UInt64) == 42)
      assert(JDI.ToInt32(UInt64.max - 12) == -13)

      assert(JDI.ToInt32(42 as UInt) == 42)
      assert(JDI.ToInt32(UInt.max - 12) == -13)

      // To Int64

      assert(JDI.ToInt64(42 as Int8) == 42)
      assert(JDI.ToInt64(-13 as Int8) == -13)

      assert(JDI.ToInt64(42 as Int32) == 42)
      assert(JDI.ToInt64(-13 as Int32) == -13)

      assert(JDI.ToInt64(42 as Int64) == 42)
      assert(JDI.ToInt64(-13 as Int64) == -13)

      assert(JDI.ToInt64(42 as Int) == 42)
      assert(JDI.ToInt64(-13 as Int) == -13)

      assert(JDI.ToInt64(42 as UInt8) == 42)
      assert(JDI.ToInt64(0xf3 as UInt8) == 243)

      assert(JDI.ToInt64(42 as UInt32) == 42)
      assert(JDI.ToInt64(0xfffffff3 as UInt32) == 4294967283)

      assert(JDI.ToInt64(42 as UInt64) == 42)
      assert(JDI.ToInt64(UInt64.max - 12) == -13)

      assert(JDI.ToInt64(42 as UInt) == 42)
      #if (arch(i386) || arch(arm))
         assert(JDI.ToInt64(UInt.max - 12) == 4294967283)  // For 32-bit systems
      #else
         assert(JDI.ToInt64(UInt.max - 12) == -13)  // For 64-bit systems
      #endif

      // To Int

      assert(JDI.ToInt(42 as Int8) == 42)
      assert(JDI.ToInt(-13 as Int8) == -13)

      assert(JDI.ToInt(42 as Int32) == 42)
      assert(JDI.ToInt(-13 as Int32) == -13)

      assert(JDI.ToInt(42 as Int64) == 42)
      assert(JDI.ToInt(-13 as Int64) == -13)

      assert(JDI.ToInt(42 as Int) == 42)
      assert(JDI.ToInt(-13 as Int) == -13)

      assert(JDI.ToInt(42 as UInt8) == 42)
      assert(JDI.ToInt(0xf3 as UInt8) == 243)

      assert(JDI.ToInt(42 as UInt32) == 42)
      #if (arch(i386) || arch(arm))
         assert(JDI.ToInt(0xfffffff3 as UInt32) == -13)  // For 32-bit systems
      #else
         assert(JDI.ToInt(0xfffffff3 as UInt32) == 4294967283)  // For 64-bit systems
      #endif

      assert(JDI.ToInt(42 as UInt64) == 42)
      assert(JDI.ToInt(UInt64.max - 12) == -13)

      assert(JDI.ToInt(42 as UInt) == 42)
      assert(JDI.ToInt(UInt.max - 12) == -13)

      // To UInt8

      assert(JDI.ToUInt8(42 as Int8) == 42)
      assert(JDI.ToUInt8(-13 as Int8) == 0xf3)

      assert(JDI.ToUInt8(42 as Int32) == 42)
      assert(JDI.ToUInt8(-13 as Int32) == 0xf3)

      assert(JDI.ToUInt8(42 as Int64) == 42)
      assert(JDI.ToUInt8(-13 as Int64) == 0xf3)
      assert(JDI.ToUInt8(Int64.max - 12) == 0xf3)

      assert(JDI.ToUInt8(42 as Int) == 42)
      assert(JDI.ToUInt8(-13 as Int) == 0xf3)
      assert(JDI.ToUInt8(Int.max - 12) == 0xf3)

      assert(JDI.ToUInt8(42 as UInt8) == 42)
      assert(JDI.ToUInt8(0xf3 as UInt8) == 0xf3)

      assert(JDI.ToUInt8(42 as UInt32) == 42)
      assert(JDI.ToUInt8(0xfffffff3 as UInt32) == 0xf3)

      assert(JDI.ToUInt8(42 as UInt64) == 42)
      assert(JDI.ToUInt8(UInt64.max - 12) == 0xf3)

      assert(JDI.ToUInt8(42 as UInt) == 42)
      assert(JDI.ToUInt8(UInt.max - 12) == 0xf3)

      // To UInt32

      assert(JDI.ToUInt32(42 as Int8) == 42)
      assert(JDI.ToUInt32(-13 as Int8) == 0xfffffff3)

      assert(JDI.ToUInt32(42 as Int32) == 42)
      assert(JDI.ToUInt32(-13 as Int32) == 0xfffffff3)

      assert(JDI.ToUInt32(42 as Int64) == 42)
      assert(JDI.ToUInt32(-13 as Int64) == 0xfffffff3)
      assert(JDI.ToUInt32(Int64.max - 12) == 0xfffffff3)

      assert(JDI.ToUInt32(42 as Int) == 42)
      assert(JDI.ToUInt32(-13 as Int) == 0xfffffff3)
      #if (arch(i386) || arch(arm))
         assert(JDI.ToUInt32(Int.max - 12) == 0x7ffffff3)  // For 32-bit systems
      #else
         assert(JDI.ToUInt32(Int.max - 12) == 0xfffffff3)  // For 64-bit systems
      #endif

      assert(JDI.ToUInt32(42 as UInt8) == 42)
      assert(JDI.ToUInt32(0xf3 as UInt8) == 0xf3)

      assert(JDI.ToUInt32(42 as UInt32) == 42)
      assert(JDI.ToUInt32(0xfffffff3 as UInt32) == 0xfffffff3)

      assert(JDI.ToUInt32(42 as UInt64) == 42)
      assert(JDI.ToUInt32(UInt64.max - 12) == 0xfffffff3)

      assert(JDI.ToUInt32(42 as UInt) == 42)
      assert(JDI.ToUInt32(UInt.max - 12) == 0xfffffff3)

      // To UInt64

      assert(JDI.ToUInt64(42 as Int8) == 42)
      assert(JDI.ToUInt64(-13 as Int8) == 0xfffffffffffffff3)

      assert(JDI.ToUInt64(42 as Int32) == 42)
      assert(JDI.ToUInt64(-13 as Int32) == 0xfffffffffffffff3)

      assert(JDI.ToUInt64(42 as Int64) == 42)
      assert(JDI.ToUInt64(-13 as Int64) == 0xfffffffffffffff3)
      assert(JDI.ToUInt64(Int64.max - 12) == (UInt64.max >> 1) - 12)

      assert(JDI.ToUInt64(42 as Int) == 42)
      assert(JDI.ToUInt64(-13 as Int) == 0xfffffffffffffff3)
      #if (arch(i386) || arch(arm))
         assert(JDI.ToUInt64(Int.max - 12) == 0x7ffffff3)  // For 32-bit systems
      #else
         assert(JDI.ToUInt64(Int.max - 12) == 0x7ffffffffffffff3)  // For 64-bit systems
      #endif

      assert(JDI.ToUInt64(42 as UInt8) == 42)
      assert(JDI.ToUInt64(0xf3 as UInt8) == 0xf3)

      assert(JDI.ToUInt64(42 as UInt32) == 42)
      assert(JDI.ToUInt64(0xfffffff3 as UInt32) == 0xfffffff3)

      assert(JDI.ToUInt64(42 as UInt64) == 42)
      assert(JDI.ToUInt64(UInt64.max - 12) == 0xfffffffffffffff3)

      assert(JDI.ToUInt64(42 as UInt) == 42)
      #if (arch(i386) || arch(arm))
         assert(JDI.ToUInt64(UInt.max - 12) == 0xfffffff3)  // For 32-bit systems
      #else
         assert(JDI.ToUInt64(UInt.max - 12) == 0xfffffffffffffff3)  // For 64-bit systems
      #endif

      // To UInt

      assert(JDI.ToUInt(42 as Int8) == 42)
      #if (arch(i386) || arch(arm))
         assert(JDI.ToUInt(-13 as Int8) == 0xfffffff3)  // For 32-bit systems
      #else
         assert(JDI.ToUInt(-13 as Int8) == 0xfffffffffffffff3)  // For 64-bit systems
      #endif

      assert(JDI.ToUInt(42 as Int32) == 42)
      #if (arch(i386) || arch(arm))
         assert(JDI.ToUInt(-13 as Int32) == 0xfffffff3)  // For 32-bit systems
      #else
         assert(JDI.ToUInt(-13 as Int32) == 0xfffffffffffffff3)  // For 64-bit systems
      #endif

      assert(JDI.ToUInt(42 as Int64) == 42)
      #if (arch(i386) || arch(arm))
         assert(JDI.ToUInt(-13 as Int64) == 0xfffffff3)  // For 32-bit systems
         assert(JDI.ToUInt(Int64.max - 12) == 0xfffffff3)
      #else
         assert(JDI.ToUInt(-13 as Int64) == 0xfffffffffffffff3)  // For 64-bit systems
         assert(JDI.ToUInt(Int64.max - 12) == 0x7ffffffffffffff3)
      #endif

      assert(JDI.ToUInt(42 as Int) == 42)
      #if (arch(i386) || arch(arm))
         assert(JDI.ToUInt(Int.max - 12) == 0x7ffffff3)  // For 32-bit systems
      #else
         assert(JDI.ToUInt(Int.max - 12) == 0x7ffffffffffffff3)  // For 64-bit systems
      #endif

      assert(JDI.ToUInt(42 as UInt8) == 42)
      assert(JDI.ToUInt(0xf3 as UInt8) == 0xf3)

      assert(JDI.ToUInt(42 as UInt32) == 42)
      assert(JDI.ToUInt(0xfffffff3 as UInt32) == 0xfffffff3)

      assert(JDI.ToUInt(42 as UInt64) == 42)
      #if (arch(i386) || arch(arm))
         assert(JDI.ToUInt(UInt64.max - 12) == 0xfffffff3)  // For 32-bit systems
      #else
         assert(JDI.ToUInt(UInt64.max - 12) == 0xfffffffffffffff3)  // For 64-bit systems
      #endif

      assert(JDI.ToUInt(42 as UInt) == 42)
      #if (arch(i386) || arch(arm))
         assert(JDI.ToUInt(UInt.max - 12) == 0xfffffff3)  // For 32-bit systems
      #else
         assert(JDI.ToUInt(UInt.max - 12) == 0xfffffffffffffff3)  // For 64-bit systems
      #endif

      print("\nTesting JDI complete.\n")
   }