如何在Swift中获取值类型或自定义结构的内存地址？ [英] How can I get the memory address of a value type or a custom struct in Swift?

问题描述

我正在努力深入了解Swift 复制值类型：

I'm trying to gain a deeper understanding of how Swift copies value types:

你的行为在你的代码中看到总是好像一个副本花了
的地方。但是，当绝对必要时，Swift仅在幕后
执行实际复制。

The behavior you see in your code will always be as if a copy took place. However, Swift only performs an actual copy behind the scenes when it is absolutely necessary to do so.

推进我的理解，我想得到一个值类型的内存地址。我尝试了unsafeAddressOf（），但这不适用于结构体，它似乎将Swift的标准库类型转换为引用类型 （例如，String被强制转换为NSString）。

To advance my understanding, I'd like to get the memory address of a value type. I tried unsafeAddressOf(), but this doesn't work with structs and it seems to cast Swift's standard library types to reference types (e.g. String is cast to NSString).

如何获取值类型的内存地址，如Int实例或Swift中的自定义结构？

推荐答案

根据Martin R的回答

According to Martin R' s answer

addressOf（）不能与struct变量一起使用。 String是一个结构，但是，当传递给期望对象的函数时，它会自动桥接到NSString。

addressOf() cannot be used with struct variables. String is a struct, however, it is automatically bridged to NSString when passed to a function expecting an object.

根据nschum的回答，您可以获得 struct 的（堆栈）地址，内置这样的类型或对象引用：

According to nschum's answer, you can get the (stack) address of a struct, build-in type or object reference like this:

import UIKit


func address(o: UnsafePointer<Void>) -> Int {
    return unsafeBitCast(o, Int.self)
}

func addressHeap<T: AnyObject>(o: T) -> Int {
    return unsafeBitCast(o, Int.self)
}


struct myStruct {
    var a: Int
}

class myClas {

}
//struct
var struct1 = myStruct(a: 5)
var struct2 = struct1
print(NSString(format: "%p", address(&struct1))) // -> "0x10f1fd430\n"
print(NSString(format: "%p", address(&struct2))) // -> "0x10f1fd438\n"

//String
var s = "A String"
var aa = s
print(NSString(format: "%p", address(&s))) // -> "0x10f43a430\n"
print(NSString(format: "%p", address(&aa))) // -> "0x10f43a448\n"

//Class
var class1 = myClas()
var class2 = class1
print(NSString(format: "%p", addressHeap(class1))) // -> 0x7fd5c8700970
print(NSString(format: "%p", addressHeap(class2))) // -> 0x7fd5c8700970

unsafeAddressOf(class1) //"UnsafePointer(0x7FD95AE272E0)"
unsafeAddressOf(class2) //"UnsafePointer(0x7FD95AE272E0)"

//Int
var num1 = 55
var num2 = num1
print(NSString(format: "%p", address(&num1))) // -> "0x10f1fd480\n"
print(NSString(format: "%p", address(&num2))) // -> "0x10f1fd488\n"

我发现的一件事是，如果 myStruct 没有价值，地址将保持不变：

One thing I found is, if myStruct has no value, the address will be retain same:

struct myStruct {

}

var struct1 = myStruct()
var struct2 = struct1
print(NSString(format: "%p", address(&struct1))) // -> ""0xa000000000070252\n""
print(NSString(format: "%p", address(&struct2))) // -> ""0xa000000000070252\n""

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