在 Swift 中：Array VS NSArray VS [AnyObject] 之间的区别

Question

正如标题所说，Array vs NSArray vs [AnyObject] 有什么区别？

此外，最推荐的解决方法是什么。我的意思是推荐的是，最简单的实现是什么。谢谢。

Answer 1

Array 是一个 Swift 结构和泛型结构，这意味着它可以是任何特定类型（Int、String、AnyObject 等）的数组

[T] 是Array<T> 的语法糖

AnyObject 是任何类的对象，包括 Objective-C 类。

NSArray 是一个 Objective-C 构造，可以容纳任何 Objective-C 对象，并且透明地映射到 Array<AnyObject> 和从 Array<AnyObject>

Answer 2

Array 是一个 struct，因此在 Swift 中它是一个 值类型。 NSArray 是一个不可变的Objective C 类，因此它是Swift 中的一个引用类型，它被桥接到Array<AnyObject>。 NSMutableArray 是 NSArray 的可变子类。

var arr : NSMutableArray = ["Pencil", "Eraser", "Notebook"]
var barr = ["Pencil", "Eraser", "Notebook"]

func foo (var a : Array<String>)
{
    a[2] = "Pen"
}

func bar (a : NSMutableArray)
{
    a[2] = "Pen"
}

foo(barr)
bar(arr)

println (arr)
println (barr)

打印：

(
    Pencil,
    Eraser,
    Pen
)
[Pencil, Eraser, Notebook]

因为foo 更改了a 的本地值，而bar 更改了引用。 如果您使用 let arr 而不是 var 与其他引用类型一样，它也将起作用。

Answer 3

使用 Krzak 的答案，这里是一个实际的例子：

// Let´s create an Array as a struct showing alternative ways
    var arrStruct = ["Pencil", "Eraser", "Notebook"]
    // or var arrStruct: [String] = ["Pencil", "Eraser", "Notebook"]
    // or var arrStruct: Array = ["Pencil", "Eraser", "Notebook"]
    // or var arrStruct = Array(["Pencil", "Eraser", "Notebook"])
    // All this alternative ways create an array as struct

    // Now let´s create a function that modifies this array struct
    func modifyArr(alternativeArr: [String]) 
    // or func modify(alternativeArr: Array<String>)
    {
        alternativeArr[2] = "Pen" // compilation error
        // This won´t work. In swift >= 3.0 all func parametes are a let variable, 
        // this means alternativeArr is defined as a let. What one has to do is 
        // create a local variable and copy the value.

        var localAlternativeArr = alternativeArr
        // or var localAlternativeArr: [String] = alternativeArr
        // or var localAlternativeArr: Array = alternativeArr

        // now we can change it.
        localAlternativeArr[2] = "Pen"
        print(localAlternativeArr) // ["Pencil", "Eraser", "Pen"]
        print(alternativeArr) // ["Pencil", "Eraser", "Notebook"]
    }

    modifyArr(alternativeArr: arrStruct)
    print(arrStruct) // ["Pencil", "Eraser", "Notebook"]

    // Since the arrStruct is a struct every time we assign to another variable or 
    // pass it as a func argument a copy is made.



// Now let´s create as an NSMutableArray
    var arrClass: NSMutableArray = ["Pencil", "Eraser", "Notebook"]
    // or var arrStruct = NSMutableArray(array: ["Pencil", "Eraser", "Notebook"])
    // All this create an NSMutableArray as a class

    // Now let´s create a function that modifies this array struct
    func modifyArr(alternativeArr: NSMutableArray)
    {
        alternativeArr[2] = "Pen"
        print(alternativeArr)
        // (
        //   Pencil,
        //   Eraser,
        //   Pen
        // )
    }

    modifyArr(alternativeArr: arrClass)
    print(arrClass)
    // (
    //   Pencil,
    //   Eraser,
    //   Pen
    // )

    // Since the arrClass is a class everytime we assign to another variable or 
    // pass it as a func argument is passed by reference. Means that any change
    // inside modifyArr is going to change the arrClass outside. The change 
    // is made in the same pointer.

Answer 4

加上@Krzak 的出色回答，这就是原因

print(NSArray().object(at: 1))   // Triggers an UnmanagedException

2018-11-09 11:38:08.798088-0600 AppName[38786:10497909] * 由于未捕获的异常“NSRangeException”而终止应用程序，原因：“* -[__NSArray0 objectAtIndex:]：空 NSArray' 超出范围的索引 1'

和

print(Array<Int>()[1])  // Halts with "Thread 1: Fatal error: Index out of range"

这种对错误的不同处理帮助我理解了其中的区别.....e