UnsafeMutablePointer Warning with Swift 5

Question

I had this:

let alphaPtr = UnsafeMutablePointer<vImagePixelCount>(mutating: alpha) as UnsafeMutablePointer<vImagePixelCount>?

Which now I get the warning:

Initialization of 'UnsafeMutablePointer' (aka 'UnsafeMutablePointer') results in a dangling pointer

Detailed warning consists of:

1. Implicit argument conversion from '[vImagePixelCount]' (aka 'Array') to 'UnsafePointer' (aka 'UnsafePointer') produces a pointer valid only for the duration of the call to 'init(mutating:)'

2. Use the 'withUnsafeBufferPointer' method on Array in order to explicitly convert argument to buffer pointer valid for a defined scope

Is there a way around this?

Answer 1

Try this

var bytes = [UInt8]()
let uint8Pointer = UnsafeMutablePointer<UInt8>.allocate(capacity: bytes.count)
uint8Pointer.initialize(from: &bytes, count: bytes.count)

Answer 2

It was never safe to do this, and the compiler now is warning you more aggressively.

let alphaPtr = UnsafeMutablePointer ...

At the end of this line, alphaPtr is already invalid. There is no promise that what it points to is still allocated memory.

Instead, you need to nest whatever usage you need into a withUnsafeMutablePointer() (or withUnsafePointer()) block. If you cannot nest it into a block (for example, if you were storing the pointer or returning it), there is no way to make that correct. You'll have to redesign your data management to not require that.