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，什么是最简单的实现。谢谢。

Answer 1

Array 是一个 Swift 构造和泛型结构，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 class 的对象，包括 Objective-C classes.

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

和从 Array<AnyObject>

映射

Answer 2

Array是一个结构，因此它是Swift中的值类型。 NSArray是不可变的Objective Cclass，因此它是[=38=中的引用类型 ] 并桥接到 Array<AnyObject>。 NSMutableArray 是 NSArray 的可变子 class。

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，它也会起作用。

Answer 3

使用 Krzak 答案，这是一个实际示例：

// 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

添加到@Krzak 的出色回答，这就是为什么

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

2018-11-09 11:38:08.798088-0600 AppName[38786:10497909] * 由于未捕获的异常终止应用程序 'NSRangeException'，原因：'* -[__NSArray0 objectAtIndex:]：索引 1 超出空 NSArray 的范围'

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方式帮助我理解了差异..... e

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

in Swift: Difference between Array VS NSArray VS [AnyObject]

collections

ios

data-structures

swift