如何通过忽略它在Swift中的相关值来比较枚举和相关联的值？ [英] How to compare enum with associated values by ignoring its associated value in Swift?

问题描述

阅读如何测试Swift枚举的平等性与相关值，我实现了以下枚举：

 枚举CardRank {
 case Number 
 case Jack 
 case Queen 
 case King 
 case Ace 
} 
 
 func ==（a：CardRank，b：CardRank） > bool {
 switch（a，b）{
 case（.Number（let a），.Number（let b））其中a == b：return true 
 case .jack）：return true 
 case（.Queen，.Queen）：return true 
 case（.King，.King）：return true 
 case（.Ace，.Ace）：return true 
 default：return false 
} 
} 
  

代码工程：

 让卡：CardRank = CardRank.Jack 
如果卡== CardRank.Jack {
 print（You played a jack！）
} else if card == CardRank.Number（2）{
 print（A two can not be played in this time。 } 
  

但是，这不会编译：

  let number = CardRank.Number（5）
 if number == CardRank.Number {
 print（You must play a face card！ b $ b} 
  

...并显示以下错误讯息：

二进制运算符'=='不能应用于类型'CardRank'和'（Int） - > CardRank'的操作数

我假设这是因为它期望一个完整的类型和 CardRank.Number 不指定整个类型，而 CardRank.Number（2）没有。但是，在这种情况下，我希望它匹配任何号码;

显然我可以使用switch语句，但是实现 == 操作符是为了避免这种详细的解决方案：

 开关号{
 case .Number：
 print 你必须玩一张面孔卡！）
默认值：
 break 
} 
  

有没有办法比较一个枚举和相关的值，而忽略它的相关值？

可以将 == 方法中的情况更改为 case（.Number，.Number）：return true 虽然它会正确返回true，我的比较仍然会看起来像它的特定数字（ number == CardRank.Number（2）;其中2是一个虚值）而不是任何号码（ number == CardRank.Number ）。

解决方案

编辑：由于Etan指出，您可以省略（_）通配符匹配， 。

---

不幸的是，我不相信有一个比你的 code>在Swift 1.2中。

但是，在Swift 2中，可以使用新的 if-case 模式匹配：

  let number = CardRank.Number（5）
如果case .Number（_）=数字{
 //是数字
} else {
 //其他
} 
  

如果你想避免冗长，你可以考虑在你的enum中添加一个 isNumber 计算属性来实现你的switch语句。 / p>

After reading How to test equality of Swift enums with associated values, I implemented the following enum:

enum CardRank {
    case Number(Int)
    case Jack
    case Queen
    case King
    case Ace
}

func ==(a: CardRank, b: CardRank) -> Bool {
    switch (a, b) {
    case (.Number(let a), .Number(let b))   where a == b: return true
    case (.Jack, .Jack): return true
    case (.Queen, .Queen): return true
    case (.King, .King): return true
    case (.Ace, .Ace): return true
    default: return false
    }
}

The following code works:

let card: CardRank = CardRank.Jack
if card == CardRank.Jack {
    print("You played a jack!")
} else if card == CardRank.Number(2) {
    print("A two cannot be played at this time.")
}

However, this doesn't compile:

let number = CardRank.Number(5)
if number == CardRank.Number {
    print("You must play a face card!")
}

... and it gives the following error message:

Binary operator '==' cannot be applied to operands of type 'CardRank' and '(Int) -> CardRank'

I'm assuming this is because it's expecting a full type and CardRank.Number does not specify an entire type, whereas CardRank.Number(2) did. However, in this case, I want it to match any number; not just a specific one.

Obviously I can use a switch statement, but the whole point of implementing the == operator was to avoid this verbose solution:

switch number {
case .Number:
    print("You must play a face card!")
default:
    break
}

Is there any way to compare an enum with associated values while ignoring its associated value?

Note: I realize that I could change the case in the == method to case (.Number, .Number): return true, but, although it would return true correctly, my comparison would still look like its being compared to a specific number (number == CardRank.Number(2); where 2 is a dummy value) rather than any number (number == CardRank.Number).

解决方案

Edit: As Etan points out, you can omit the (_) wildcard match to use this more cleanly.

---

Unfortunately, I don't believe that there's an easier way than your switch approach in Swift 1.2.

In Swift 2, however, you can use the new if-case pattern match:

let number = CardRank.Number(5)
if case .Number(_) = number {
    // Is a number
} else {
    // Something else
}

If you're looking to avoid verbosity, you might consider adding an isNumber computed property to your enum that implements your switch statement.

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