相同对象的地址不同。为什么? [英] Same object different address. Why?
问题描述
由于 f
和 bar [42]!
指向下面代码中的相同闭包不安全的指针指向同一个地址。
他们没有。任何人都可以解释为什么?
Since both f
and bar[42]!
point to the same closure in the following code I would expect the unsafe pointers to point to the same address.
They do not. Can anyone please explain why?
澄清:我使用view memory查找withUnsafePointer在Xcode中返回的地址。
To clarify: I'm looking up the address returned by withUnsafePointer in Xcode using "view memory".
var bar = [Int : (() -> Void)]()
bar[42] = { print("foo") }
var f = bar[42]!
f() // prints "foo"
bar[42]!() // prints "foo"
withUnsafePointer(to: &f) { print( type(of: $0) ) ; print( $0 ) }
// UnsafePointer<(()) -> ()> 0x00007fff5fbff778 -> 0x100002100
withUnsafePointer(to: &bar[42]!) { print( type(of: $0) ) ; print($0) }
// UnsafePointer<(()) -> ()> 0x00007fff5fbff760 -> 0x100001d20
更新
该代码还打印出指针的值:
Update
I've updated the code to also print out the pointer's value:
var bar = [Int : (() -> Void)]()
bar[42] = { print("foo") }
var f = bar[42]!
f() // prints "foo"
bar[42]!() // prints "foo"
withUnsafePointer(to: &f) {
print( type(of: $0.pointee) )
print( $0 )
$0.withMemoryRebound(to: Int.self, capacity: 1) {
print("-> 0x\(String($0.pointee, radix: 16))")
}
}
withUnsafePointer(to: &bar[42]!) {
print( type(of: $0.pointee) )
print($0)
$0.withMemoryRebound(to: Int.self, capacity: 1) {
print("-> 0x\(String($0.pointee, radix: 16))")
}
}
在发布模式下运行此输出可提供以下输出:
Running this in Release mode gives the following output:
foo
foo
(()) -> ()
0x00007fff5fbff7d0
-> 0x100003f10
(()) -> ()
0x00007fff5fbff7d0
-> 0x100001f60
这表明编译器看到 f
和 bar [42]!
是相同的。混淆的是,同一个地址可以指向同一闭包的不同副本。
Which suggests that the compiler sees that f
and bar[42]!
are the same. What's confounding is that the same address can point to different copies of the same closure.
推荐答案
& var
是包含原始存储器位置的地址的存储器位置的地址(即,它是指针的指针)。
&var
is the address of the memory location that contains the address of the original memory location (i.e., it's a "pointer to a pointer").
因为 ff
& bar []
是两个不同的变量,它们的地址也不同。
Since ff
& bar[]
are two different variables, their adresses are differents too.
ff(18) bar(20) coolvalue(84)
[84]...[]...[84]...[].............[xxx]
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