我正在努力深入了解
Swift
copies value types：
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.
为了提高我的理解,我想得到一个值类型的内存地址.我尝试了unsafeAddressOf(),但是this doesn’t work with structs and it seems to cast Swift’s standard library types to reference types(例如String被强制转换为NSString).
解决方法
根据马丁R的回答
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,您可以获得结构,内置类型或对象引用的(堆栈)地址,如下所示：
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没有值,地址将保持不变：
struct myStruct {
}
var struct1 = myStruct()
var struct2 = struct1
print(NSString(format: "%p",address(&struct1))) // -> ""0xa000000000070252\n""
print(NSString(format: "%p",address(&struct2))) // -> ""0xa000000000070252\n""
