當涉及到相同的變量時，Swift Array內存地址發生變化

Question

我正在學習Python並希望確認Objective-C和Swift中的特定行爲。

試驗如下：

的Python

def replace(list): 
    list[0] = 3 
    print(list) 

aList = [1, 2, 3] 
print(aList) 
replace(aList) 
print(aList) 

目標C

- (void)replace:(NSMutableArray *)array { 
    array[0] = @1; 
    NSLog(@"array: %@, address: %p\n%lx", array, array, (long)&array); 
} 

NSMutableArray *array = [@[@1, @2, @3] mutableCopy]; 
NSLog(@"original: %@, address: %p \n%lx", array, array, (long)&array); 
[self replace:array]; 
NSLog(@"modified: %@, address: %p \n%lx", array, array, (long)&array); 

夫特

var numbers = [1, 2, 3] 
let replace = { (var array:[Int]) -> Void in 
    array[0] = 2 
    print("array: \(array) address:\(unsafeAddressOf(array as! AnyObject))") 
} 

print("original: \(numbers) address:\(unsafeAddressOf(numbers as! AnyObject))") 
replace(numbers) 
print("modified: \(numbers) address:\(unsafeAddressOf(numbers as! AnyObject))") 

除了Swift中的地址部分外，所有的結果都如預期般出來。在Objective-C，數組的地址留在original和modified相同，但斯威夫特的打印結果爲：

original: [1, 2, 3] address:0x00007f8ce1e092c0 
array: [2, 2, 3] address:0x00007f8ce1f0c5d0 
modified: [1, 2, 3] address:0x00007f8ce4800a10 

有我丟失的東西？

Answer 1

Swift中的數組具有值語義，而不是Python和Objective-C中數組的引用語義。你看到不同地址（和地址）的原因是每次你做一個as! AnyObject演員，你實際上告訴Swift橋接你的Array<Int>結構到NSArray的一個實例。既然你連接了三次，你會得到三個不同的地址。

---

你不應該需要考慮迅捷的數組的地址，但如果你希望（暫時）獲取數組的緩衝區的地址，你可以這樣來做：

func getBufferAddress<T>(array: [T]) -> String { 
    return array.withUnsafeBufferPointer { buffer in 
     return String(buffer.baseAddress) 
    } 
} 

這使您可以看到緩存的寫入時複製在行動：

var numbers = [1, 2, 3] 
let numbersCopy = numbers 

// the two arrays share a buffer here 
getBufferAddress(numbers)     // "0x00007fba6ad16770" 
getBufferAddress(numbersCopy)    // "0x00007fba6ad16770" 

// mutating `numbers` causes a copy of its contents to a new buffer 
numbers[0] = 4 

// now `numbers` has a new buffer address, while `numbersCopy` is unaffected 
getBufferAddress(numbers)     // "0x00007ff23a52cc30" 
getBufferAddress(numbersCopy)    // "0x00007fba6ad16770"