如果枚举值具有关联值，则测试枚举值失败? [英] Testing for enum value fails if one has associated value?

问题描述

我正在 Playground 中对此进行测试，但我不确定如何执行此操作.使用没有关联值的普通枚举，一切都很好.

I'm testing this in the Playground and I'm not sure how to do this. With a normal enum that doesn't have associated values, everything is fine.

enum CompassPoint {
    case North
    case South
    case East
    case West
}

var direction = CompassPoint.East

if direction != .West {
    println("Go West!")
}

但是，如果我的枚举之一具有关联值，则方向测试将失败并显示以下错误:找不到成员West"

However, if one of my enums has an associated value, the direction test fails with this error: could not find member 'West'

enum CompassPoint {
    case North(Int)
    case South
    case East
    case West
}

var direction = CompassPoint.East

if direction != .West {
    println("Go West!")
}

我能做些什么来允许这个测试?

What can I do to allow for this test?

推荐答案

当枚举具有 Equatable 的原始值时，它们会自动Equatable.在你的第一种情况下，原始值被假定为 Int，但如果你给它另一个特定的类型，比如 UInt32 甚至 String.

Enumerations are automatically Equatable when they have a raw value that's Equatable. In your first case, the raw value is assumed to be Int, but it would work if you'd given it another specific type like UInt32 or even String.

但是，一旦添加了关联值，就不会再发生这种与 Equatable 的自动一致性，因为您可以声明:

Once you add an associated value, however, this automatic conformance with Equatable doesn't happen any more, since you can declare this:

let littleNorth = CompassPoint.North(2)
let bigNorth = CompassPoint.North(99999)

那些是平等的吗?斯威夫特应该怎么知道?你必须告诉它，通过将 enum 声明为 Equatable 然后实现 == 运算符:

Are those equal? How should Swift know? You have to tell it, by declaring the enum as Equatable and then implementing the == operator:

enum CompassPoint : Equatable {
    case North(Int)
    case South
    case East
    case West
}

public func ==(lhs:CompassPoint, rhs:CompassPoint) -> Bool {
    switch (lhs, rhs) {
    case (.North(let lhsNum), .North(let rhsNum)):
        return lhsNum == rhsNum
    case (.South, .South): return true
    case (.East, .East): return true
    case (.West, .West): return true
    default: return false
    }
}

现在您可以测试相等或不相等，如下所示:

Now you can test for equality or inequality, like this:

let otherNorth = CompassPoint.North(2)
println(littleNorth == bigNorth)            // false
println(littleNorth == otherNorth)          // true

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