如何在Swift 4中测试具有关联值的枚举情况的等效性

发布时间：2020-12-14 04:38:40 所属栏目：百科来源：网络整理

导读：我想测试几个枚举类型变量的等价性,如下所示： enum AnEnumeration { case aSimpleCase case anotherSimpleCase case aMoreComplexCase(String)}let a1 = AnEnumeration.aSimpleCaselet b1 = AnEnumeration.aSimpleCasea1 == b1 // Should be true.let a2 =

我想测试几个枚举类型变量的等价性,如下所示：

enum AnEnumeration {
  case aSimpleCase
  case anotherSimpleCase
  case aMoreComplexCase(String)
}

let a1 = AnEnumeration.aSimpleCase
let b1 = AnEnumeration.aSimpleCase
a1 == b1 // Should be true.

let a2 = AnEnumeration.aSimpleCase
let b2 = AnEnumeration.anotherSimpleCase
a2 == b2 // Should be false.

let a3 = AnEnumeration.aMoreComplexCase("Hello")
let b3 = AnEnumeration.aMoreComplexCase("Hello")
a3 == b3 // Should be true.

let a4 = AnEnumeration.aMoreComplexCase("Hello")
let b4 = AnEnumeration.aMoreComplexCase("World")
a3 == b3 // Should be false.

可悲的是,这些都产生了这样的错误：

error: MyPlayground.playground:7:4: error: binary operator '==' cannot be applied to two 'AnEnumeration' operands
a1 == b1 // Should be true.
~~ ^  ~~

MyPlayground.playground:7:4: note: binary operator '==' cannot be synthesized for enums with associated values
a1 == b1 // Should be true.
~~ ^  ~~

翻译：如果您的枚举使用关联值,则无法测试它的等效性.

注意：如果删除了.aMoreComplexCase(和相应的测试),那么代码将按预期工作.

看起来过去人们已经决定使用运算符重载来解决这个问题：How to test equality of Swift enums with associated values.但是现在我们有了Swift 4,我想知道是否有更好的方法？或者,如果有更改使链接的解决方案无效？

谢谢！

解决方法

斯威夫特的提议

> SE-0185 Synthesizing Equatable and Hashable conformance

已被Swift 4.1(Xcode 9.3)接受并实现：

… synthesize conformance to Equatable/Hashable if all of its members are Equatable/Hashable.

因此,它就足够了

… opt-in to automatic synthesis by declaring their type as Equatable or Hashable without implementing any of their requirements.

在你的例子中 – 因为String是Equatable – 它足以声明

enum AnEnumeration: Equatable {
  case aSimpleCase
  case anotherSimpleCase
  case aMoreComplexCase(String)
}

并且编译器将合成一个合适的==运算符.

（编辑：李大同）

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