Ios Un托管和withUnsafePointer API之间的区别

以下是我使用的示例代码:

class Dummy {
    let uuid = UUID()
}

func test() {
    
    let dummy = Dummy()
    let unmangedOpaquePointer = Unmanaged.passUnretained(dummy).toOpaque()
    let fromWithUnsafeAPIPointer = withUnsafePointer(to: dummy, { UnsafeMutableRawPointer(mutating: $0) })
    print(unmangedOpaquePointer == fromWithUnsafeAPIPointer) // false
    
    let dummy1 = Unmanaged<Dummy>.fromOpaque(unmangedOpaquePointer).takeUnretainedValue()
    let dummy2 = fromWithUnsafeAPIPointer.assumingMemoryBound(to: Dummy.self).pointee
    let dummy3 = Unmanaged<Dummy>.fromOpaque(fromWithUnsafeAPIPointer).takeUnretainedValue()
    let dummy4 = unmangedOpaquePointer.assumingMemoryBound(to: Dummy.self).pointee
    
    print(dummy1 === dummy2) // true
    print(dummy1 === dummy3) // EXC_BAD_ACCESS
    print(dummy2 === dummy4) // EXC_BAD_ACCESS
}

test()

• 不同的UnsafeMutableRawPointer实例

print(unmangedOpaquePointer == fromWithUnsafeAPIPointer) // false

上述代码片段的结果为"假".这是意料之中的.unmangedOpaquePointer和fromWithUnsafeAPIPointer是UnsafeMutableRawPointer的不同实例，因此它们不相等. 然而，它们在这里都指向相同的对象dummy.如果unmangedOpaquePointer == fromWithUnsafeAPIPointer不是实现这个事实的正确方法，我该如何测试这个事实呢？

• API调用应该配对吗？为什么？从Unmanaged个API返回的UnsafeMutableRawPointer和withUnsafePointer个API之间有什么区别？

print(dummy1 === dummy2) // true

print调用表明从两个指针检索到的dummy 1和dummy 2相同(相同的对象实例).然而，dummy1 === dummy3和dummy2 === dummy4不是运行时有效的表达(导致它们都崩溃). 因此，通过调用Unmanaged API返回的指针似乎只应该与Unmanaged API一起使用，以检索指针指向的值.withUnsafePointer个API也是如此.为什么？

在@Sweeper的帮助下，我测试了示例代码的另一个版本:

class Dummy {
    let uuid = UUID()
}

func test() {

    var dummy = Dummy()
    let unmangedOpaquePointer = Unmanaged.passUnretained(dummy).toOpaque()
    withUnsafeMutablePointer(to: &dummy) {
        let fromWithUnsafeAPIPointer = UnsafeMutableRawPointer($0)
        print(unmangedOpaquePointer == fromWithUnsafeAPIPointer) // false
        
        let dummy1 = Unmanaged<Dummy>.fromOpaque(unmangedOpaquePointer).takeUnretainedValue()
        let dummy2 = fromWithUnsafeAPIPointer.assumingMemoryBound(to: Dummy.self).pointee
        let dummy3 = Unmanaged<Dummy>.fromOpaque(fromWithUnsafeAPIPointer).takeUnretainedValue()
        let dummy4 = unmangedOpaquePointer.assumingMemoryBound(to: Dummy.self).pointee

        print(dummy1 === dummy2) // true
        print(dummy1 === dummy3) // EXC_BAD_ACCESS
        print(dummy2 === dummy4) // EXC_BAD_ACCESS
    }
}

test()

这纠正了使用withUnsafePointer个API的错误方式.但结果是一样的.