设置为属性时，Swift枚举会失去初始化值？ [英] Swift enum loses initialized values when set as a property?

问题描述

我找到了一个解决方案，但是这个问题让我很烦恼，我以为我会分享，以防其他人遇到同样的问题。很想知道为什么会发生这种情况。在下面的代码中，当它是一个局部变量时，我可以在类初始化器中打开枚举。我将枚举值存储到属性中。但是，当我尝试在下面的示例中以不同的方法（名为bar（））打开存储的属性（名为foo）时，我收到编译器警告和错误，该成员不被识别。似乎知道foo是一个MyEnum类型，但不知道.ABC，.DEF和.GHI是成员。

I've found a work-around, but this problem is vexing me and I thought I'd share in case anyone else is having the same problem. Would love to know why this is happening. In the code below, I can switch on the enum just fine during the class initializer when it's a local variable. I store the enum value into a property. But when I try to switch on the stored property (named foo) in a different method (named bar()) in the example below - I get compiler warnings and an error that the member(s) are not recognized. It seems to know that foo is a MyEnum type, but doesn't know that .ABC, .DEF, and .GHI are members.

enum MyEnum {
    case ABC, DEF, GHI
}

class MyClass : NSObject {

    var foo : MyEnum!

    convenience init(foo: MyEnum) {

        self.init()

        self.foo = foo

        switch foo {

        case .ABC: println("ABC foo")
        case .DEF: println("DEF foo")
        case .GHI: println("GHI foo")
        default: println("no foo")

        }
    }

    func bar() {

        switch foo {

        case .ABC: println("ABC foo")
        case .DEF: println("DEF foo")
        case .GHI: println("GHI foo")
        default: println("no foo")

        }
    }
}

解决方法是说：

switch foo as MyEnum { }

或在方法中声明一个局部变量，如

or declare a local variable in the method like

let x : MyEnum = foo

switch x {  }

再次，我很高兴找到一个解决方法，但一定要知道这是否是exp如果需要向苹果提交雷达。这是Xcode 6.2，BTW。

Again, glad I found a workaround, but would sure like to know if this is the expected behavior or if a radar needs to be filed with Apple. This is Xcode 6.2, BTW.

推荐答案

属性 foo code> MyEnum ，但 ImplicitlyUnwrappedOptional< MyEnum> aka MyEnum！。与许多其他情况不同， switch 不会隐式解开它。

Property foo is not MyEnum, but ImplicitlyUnwrappedOptional<MyEnum> aka MyEnum!. Unlike many other cases, switch does not implicitly unwrap it.

您必须手动解开它：

    if let foo = foo {
        switch foo {
        case .ABC: println("ABC foo")
        case .DEF: println("DEF foo")
        case .GHI: println("GHI foo")
        default: println("no foo")
        }
    }
    else {
        println("nil foo")
    }

如果您确定 foo 不是！ c> code>，

OR force unwrap with ! if you are sure foo is not nil, :

    switch foo! {
    case .ABC: println("ABC foo")
    case .DEF: println("DEF foo")
    case .GHI: println("GHI foo")
    default: println("no foo")
    }

或与 ImplicitlyUnwrappedOptional& Enum> 原样：

    switch foo {
    case .Some(.ABC): println("ABC foo")
    case .Some(.DEF): println("DEF foo")
    case .Some(.GHI): println("GHI foo")
    default: println("no foo")
    }

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