在 Swift 中对数组进行冒泡排序，交换时出现编译器错误 [英] Bubble sorting an array in Swift, compiler error on swap

问题描述

我为纸牌游戏编写了一个非常简单的冒泡排序.它接受一组卡片"对象，每个对象都有一个顺序"属性，该属性指示要针对相关游戏进行排序的值.

I wrote a really simple bubble sort for a card game. It takes an array of "Card" objects, each of which has a an "order" attribute which indicates the value to be sorted against for the game in question.

以下代码在 Swift Beta 1 和 Beta 6 之间的一段时间内停止编译，我不确定为什么.

The following code stopped compiling some time between Swift Beta 1 and Beta 6, and I'm not exactly sure why.

 ///Sort the cards array by order
  func sortCards(cards: Array<Card>) -> Array<Card> {
    var sorted = false
    while sorted == false {
      sorted = true
      for i in 0...cards.count - 2 {
        if cards[i].order > cards[i+1].order {
          sorted = false
          var first = cards[i]
          var second = cards[i + 1]
          cards[i] = second    //ERROR
          cards[i + 1] = first //ERROR
        }
      }
    }
    return cards
  }

发生交换的那几行带有一个非常神秘的消息:

The lines where the swap occurs bombs out with a very cryptic message:

@!value $T5 与 'Card' 不同

发生了什么变化，我在这里做错了什么?

What changed, and what am I doing wrong here?

额外问题:我应该如何理解错误消息?

Bonus question: How am I supposed to understand the error message?

推荐答案

函数参数默认为常量(就像用 let 声明一样).如果要修改函数内部的参数，必须将其声明为变量:

Function parameters are by default constant (as if declared with let). If you want to modify the parameter inside your function, you have to declare it as a variable:

func sortCards(var cards: Array<Card>) -> Array<Card> { ...

注意只修改了局部参数cards，而不是传入的数组函数的参数(这似乎是您的意图，因为函数返回一个新数组.

Note that only the local parameter cards is modified, not the array passed as an argument to the function (which seems to be your intention because the function returns a new array).

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