swift - 无法通过下标快速分配

Question

我正在尝试在 Swift 中实现通用算法。

即使我没有将数字定义为 let 变量，但我收到以下错误:

cannot assign through subscript: 'numbers' is a 'let' constant numbers[i] = maxNumber

我的实现如下:

func InsertionSort (numbers : [Int]) -> [Int]
{
    var maxNumber  = 0
    var j = 0
    var size = numbers.count-1

    for (i,number) in numbers.enumerated()
    {
        j = i + 1
        for index in j...size
        {
            if numbers[index] > number
            {
                maxNumber = numbers[index]
                numbers[index] = numbers[i]
                // error is thrown in the following line
                numbers[i] = maxNumber
            }
        }
    }

    return numbers
}

Answer 1

默认情况下参数是不可变的。要使参数可变，您需要添加一个 inout 修饰符。

但是，看到您的方法返回 一个数组，您可能不希望参数也被修改。您应该制作参数的副本，修改它，然后返回副本:

func InsertionSort (numbers : [Int]) -> [Int]
{
    var maxNumber  = 0
    var j = 0
    let size = numbers.count-1
    var numbersCopy = numbers // <------ note this line

    for (i,number) in numbers.enumerated()
    {
        j = i + 1
        for index in j...size
        {
            if numbers[index] > number
            {
                maxNumber = numbers[index]

                // note how I modified the copy here
                numbersCopy[index] = numbers[i]
                numbersCopy[i] = maxNumber
            }
        }
    }

    return numbersCopy
}