Int to UInt (and vice versa) bit casting in Swift

Question

I am looking for a direct way to bit cast the bit values of an Int to UInt and vice versa. For example (using the 8 bits integers for simplicity) I want to achieve the following:

let unsigned: UInt8 = toUInt8(-1)  // unsigned is 255 or 0xff let signed:   Int8  = toInt8(0xff) // signed is -1  

At first I came out with the following solution:

let unsigned = unsafeBitCast(Int8(-1), UInt8.self) let signed   = unsafeBitCast(UInt8(0xff), Int8.self) 

But Apple in the "unsafeBitCast()" documentation states the following:

.. Caution:: Breaks the guarantees of Swift's type system; use with extreme care. There's almost always a better way to do anything.

Does anyone have the better way?

Answer 1

You can do:

let unsigned = UInt8(bitPattern: Int8(-1)) // -> 255 let signed   = Int8(bitPattern: UInt8(0xff)) // -> -1 

Many similar initializers exist:

extension Int8 {     init(_ v: UInt8)     init(_ v: UInt16)     init(truncatingBitPattern: UInt16)     init(_ v: Int16)     init(truncatingBitPattern: Int16)     init(_ v: UInt32)     init(truncatingBitPattern: UInt32)     init(_ v: Int32)     init(truncatingBitPattern: Int32)     init(_ v: UInt64)     init(truncatingBitPattern: UInt64)     init(_ v: Int64)     init(truncatingBitPattern: Int64)     init(_ v: UInt)     init(truncatingBitPattern: UInt)     init(_ v: Int)     init(truncatingBitPattern: Int)     init(bitPattern: UInt8) }