阅读How to test equality of Swift enums with associated values之后,我实现了以下枚举:
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
}
}
以下代码有效:
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.")
}
然而,这并不能编译:
let number = CardRank.Number(5)
if number == CardRank.Number {
print("You must play a face card!")
}
... 并给出以下错误信息:
Binary operator '==' cannot be applied to operands of type 'CardRank' and '(Int) -> CardRank'
我假设这是因为它需要一个完整的类型,而CardRank.Number
没有指定一个完整的类型,而CardRank.Number(2)
指定了.然而,在本例中,我希望它匹配any号;不仅仅是一个具体的问题.
显然,我可以使用switch语句,但实现==
运算符的全部目的是避免这种冗长的解决方案:
switch number {
case .Number:
print("You must play a face card!")
default:
break
}
是否有任何方法可以将枚举与关联值进行比较,同时忽略其关联值?
Note:我意识到我可以将==
方法中的case改为case (.Number, .Number): return true
,但是,尽管它会正确返回true,但我的比较看起来仍然像是与特定数字(number == CardRank.Number(2)
;其中2是一个伪值)进行比较,而不是与any数字(number == CardRank.Number
)进行比较.