Swift（beta 3）“NSDictionary？不符合协议'Equatable'" [英] Swift (beta 3) "NSDictionary? does not conform to protocol 'Equatable'"

问题描述

自从更新到最新的Xcode 6 DP3以来，我的Swift代码中出现了一些警告和错误。大多数已通过采用新更改的语法解决，但有一个错误似乎很奇怪。

I've had a fair few warnings and errors in my Swift code since updating to the latest Xcode 6 DP3. Most have been resolved by adopting the newly changed syntax however there is one error which seems strange.

以下代码给出错误输入'NSDictionary？ '不符合协议'Equatable'：

if (launchOptions != nil && launchOptions![UIApplicationLaunchOptionsRemoteNotificationKey] != nil) {

有没有人有解决方案？我可能在这里忽略了一些简单的东西..！

Does anyone have a solution? I'm probably overlooking something simple here..!

谢谢

推荐答案

Beta 3中存在回归导致可选< T> 无法与 nil 进行比较，如果 T 不是 Equatable 或可比较。

There is a regression in Beta 3 causing that Optional<T> cannot be compared with nil if T is not Equatable or Comparable.

这是由于删除了定义了相等运算符的 _Nil 类型而导致的错误。 nil 现在是一个文字。该问题已由Chris Lattner在 Apple Dev论坛上确认

It's a bug caused by the removal of the _Nil type for which the equality operators were defined. nil is now a literal. The bug has been confirmed by Chris Lattner on Apple Dev Forums

一些解决方法：

您仍然可以使用 .getLogicValue（）

if launchOptions.getLogicValue() && ... {

或直接

if launchOptions && ... { //calls .getLogicValue()

或者您可以使用Javascript对象布尔 解决方案

or you can use the "Javascript object to boolean" solution

var bool = !!launchOptions

（第一个！调用 getLogicValue 并否定，第二个！再次否定）

(first ! calls the getLogicValue and negates, the second ! negates again)

或者，您可以自己定义这些相等运算符，直到它们修复它：

or, you can define those equality operators by yourself until they fix it:

//this is just a handy struct that will accept a nil literal
struct FixNil : NilLiteralConvertible {
    static func convertFromNilLiteral() -> FixNil {
        return FixNil()
    }
}

//define all equality combinations
func == <T>(lhs: Optional<T>, rhs: FixNil) -> Bool {
    return !lhs.getLogicValue()
}

func != <T>(lhs: Optional<T>, rhs: FixNil) -> Bool {
    return lhs.getLogicValue()
}

func == <T>(lhs: FixNil, rhs: Optional<T>) -> Bool {
    return !rhs.getLogicValue()
}

func != <T>(lhs: FixNil, rhs: Optional<T>) -> Bool {
    return rhs.getLogicValue()
}

示例：

class A {
}

var x: A? = nil

if x == nil {
    println("It's nil!")
}
else {
    println("It's not nil!")
}

但是，这种解决方法可能会导致其他微妙的问题（它可能同样有效）到Beta 2中的 _Nil 类型已被删除，因为它导致了问题......）。

However, this workaround might cause other subtle problems (it probably works similarily to the _Nil type in Beta 2 which was removed because it was causing problems...).

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