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;

我已经在使用此指针作为context中的observeValueForKeyPath:ofObject:change:context:的KVO的Objective-C代码库中看到过这种情况。

是否可以指向指向Swift中为该指针分配的内存空间的指针，还是手动为指针分配内存？在初始化期间尝试将指针指向其自身的内存值会导致错误（如预期的那样）：

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

语言中不存在

CMutableVoidPointer，并且不推荐初始化指针（UnsafeMutablePointer<Void>()），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上：

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

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

斯威夫特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($0) }

将UnsafeMutablePointer <void>指向自身

1 个答案: