将 UnsafeMutablePointer<Void> 指向自身

Question

在C中，指针指向分配给指针的内存位置是有效的：

static void * SomeContext = &SomeContext;

我已经看到它在 Objective-C 代码库中与 KVO 一起使用，通过将此指针用作 observeValueForKeyPath:ofObject:change:context:.

中的 context

是否可以将指针指向在 Swift 中为该指针分配的内存 space，或者手动为指针分配内存？在初始化期间试图将指针指向自身的内存值会导致错误（如预期）：

var somePointer: UnsafeMutablePointer<Void> = &somePointer // Error: Variable used within its own initial value

CMutableVoidPointer 不再存在于语言中，初始化指针 (UnsafeMutablePointer<Void>()) 已弃用，只需将指针设置为 nil.

可能是这样的：

var ptr = malloc(sizeof(UnsafeMutablePointer<Void>))
ptr = &ptr // Error: error: cannot assign value of type 'inout UnsafeMutablePointer<Void>' (aka 'inout UnsafeMutablePointer<()>') to type 'UnsafeMutablePointer<Void>' (aka 'UnsafeMutablePointer<()>')

Answer 1

在 Swift 3:

var somePointer = UnsafeMutableRawPointer(bitPattern: 1)!
somePointer = UnsafeMutableRawPointer(mutating: &somePointer)

print(somePointer)
print(somePointer.load(as: UnsafeMutableRawPointer.self))
// Output of both should be the same.

Swift 2:

Use withUnsafePointer 获取指向变量的指针。然后将其分配给自己。

var somePointer: UnsafeMutablePointer<Void> = nil
withUnsafePointer(&somePointer) { somePointer = UnsafeMutablePointer([=11=]) }

将 UnsafeMutablePointer<Void> 指向自身

Point an UnsafeMutablePointer<Void> to itself

unsafe-pointers

swift