Declaring self-referencing pointers in Swift [duplicate]

问题

This question already has answers here:

Adding observer for KVO without pointers using Swift (5 answers)

Closed 4 years ago.

What would be the equivalent in swift of this Obj-C code?

I'm guessing something with CMutableVoidPointer

static void *CapturingStillImageContext = &CapturingStillImageContext;

回答1:

Probably something like this:

var CapturingStillImageContext: COpaquePointer = nil
withUnsafePointer(&CapturingStillImageContext) {
    CapturingStillImageContext = COpaquePointer($0) }

回答2:

CMutableVoidPointer isn't available anymore as of Beta 3. Theres UnsafePointer and ConstUnsafePointer - you can declare it this way:

let CapturingStillImageContext = UnsafePointer<()>()

回答3:

I've been using this technique, but it would be nice to find a more elegant solution:

var SelfReferencingKey = initialize_SelfReferencingKey()

func initialize_SelfReferencingKey() -> UnsafePointer<()> {
    return withUnsafePointer(&SelfReferencingKey, { UnsafePointer($0) } )
}

来源：https://stackoverflow.com/questions/24628304/declaring-self-referencing-pointers-in-swift